No longer do many cities in United States have a river as the focal point of urban life
... is grammatically equivalent to ...
Many cities in United States no longer have a river as the focal point of urban life

also
Only yesterday were we told about the layoffs
... is equivalent to ...
We were told about the layoffs only yesterday

the primary difference between the examples in each pair is rhetorical. in particular, the first one in each pair -- the one that places the adverb (only yesterday, no longer) in front -- would be written that way in order to emphasize the meaning of that adverb. from the standpoint of grammar, there is essentially no difference.

the correct answer here is still pretty ugly, so let's criticize the four incorrect choices.

choice a:
faulty comparison:
'unlike many u.s. cities, ... the river in san antonio...' --> can't compare cities to a river

choice b:
comparison isn't so good:
the second part should start directly with 'the river' (instead of 'in san antonio the river...'), so that the comparison is more clear.
much more importantly, poor use of the relative pronoun 'which':
'...cities in the united states, which is no longer the focal point...'
relative pronouns like which, by default, refer to the noun that's closest to the left, which in this case is the united states. therefore, this relative pronoun is used in a way that's either ambiguous (if you allow it to potentially refer to other nouns) or just plain wrong (if you follow the rule strictly).

choice c:
faulty comparison again
'the river...' is being compared to san antonio.

choice d:
drastic change in meaning
this sentence has completely gotten rid of any reference to the concept of 'no longer'. while all the other sentences say that things have changed, this sentence presents the situation as if it's always been that way.

"instead of" is generally restricted to nouns.

"rather than" can be used for essentially any part of speech at all.

they moved stiffly rather than gracefully (adverbs)
they moved to the left rather than to the right (prepositional phrases)
the car was red rather than blue (adjectives)
i bought a car rather than a truck (nouns) <–– this is the only sentence here that would work with 'instead of'
he chose to leave rather than continue arguing (infinitives)

Either "using" or "by using" would be fine.

Note that "using" is more flexible than other __ing words.
In fact, it's best to think of "using" as belonging to two different categories of words:
1/ It's an __ing word (= it can be used like other __ing words);
2/ It's a preposition, with a meaning largely similar to that of "with".
This is usage #2.

By the way, this distinction is immaterial here, because choice C (= the only choice with "by using") contains blatant non-parallelism.

Takeaways:
— Parallelism is the #1 error in SC. DO NOT think about other things before thinking about parallelism!
— If you're thinking about a small, nit-picky issue, STOP and ask yourself, "Am I being distracted from a larger issue?"
Here, "using"/"by using" is a distraction meant to take your eyes off of the parallelism. Looks like they got you.

SUBJECT + ACTIVE VERB + BY + NOUN is generally incorrect.**
SUBJECT + ACTIVE VERB + BY + VERBing is generally correct, if "VERBing" is the method or process by which the ACTIVE VERB is carried out.
e.g.
i prepared for the test by studying flash cards --> CORRECT
i prepared for the test by the study of flash cards --> INCORRECT

on the other hand,
SUBJECT + PASSIVE VERB + BY + NOUN is an absolutely fundamental form, if the NOUN is the thing/person that did the action to the SUBJECT.
e.g.
james was seen by two witnesses. --> CORRECT
--
** the only exceptions to this occur in the case of special idiomatic expressions. for instance, "by candlelight" is a known idiomatic expression, so constructions such as "i studied by candlelight" are correct.

Ron：you can't just make random words parallel. parallelism is restricted to words that actually represent PARALLEL CONCEPTS in the sentence.

the two MAIN VERBS in the sentence are "call" and "attract". THOSE two verbs should be parallel.
"using" is a MODIFIER that modifies the "call" clause. this is as it should be, since "using" is a subordinate idea (it just describes the way in which the calling is done - it's not another action parallel to the calling).

so "call" and "attract" SHOULD be parallel; these two verbs should NOT be parallel to "using".

C错误在于picture内容是ocean current的pattern和cause而不是ocean current、pattern、cause三者一起，三者性质不同，不能并列。

A so as用法错误

Thai village crafts, as with other cultures, have developed through the principle that form follows function and incorporate readily available materials fashioned using traditional skills.

这句话的主句crafts have developed ... and incorporate... 一个是完成时态，一个是一般现在时，为什么说B选项要用have done呢？那后面的一般现在时不用管了吗？

Clearly price promotions are generally run at a loss, otherwise there would be more of them.
evidence for price promotions' "effect on the bottom line" ：价格促销影响bottom line的证据：如果不是occur in loss, 价格促销会更多

D：有left stroke就一定会有语言损害

像这种有交集的CR题，可以考虑画图法做：
1. Asthma is less common, 所以Asthma是小圆
2. Hay fever is more common，所以是大圆
3. 一个小圆和一个大圆交叉，交叉面积占小圆的95%，那么交叉面积占大圆肯定小于大圆的95%
D推不出来

E错在后半句：需要被更改的是文中的strategy，而不是BD2所描述的situation
C：the second is a judgment providing a basis for the argument's advocacy of a particular strategy. 该advocacy可以是正向的，也可以是负向的

in (b) and (d), the pronoun "its" is completely stranded; there's no antecedent for it anywhere.
takeaway:
if a sentence contains a COMPOUND NOUN (X and Y), you CANNOT use a pronoun to refer to just X or just Y, unless you use "the former" or "the latter" to make the distinction explicit.

* see #109 in the yellow og11. in that problem, all four of the incorrect answers try to use the singular pronoun "his" to refer to 1/2 of a compound noun. that's forbidden.
DO NOT post additional details of that problem here.

* this rule still holds even if X and Y take separate pronouns.
for instance:
joe and jane both have prestigious jobs, although her salary is much higher
would still be disallowed under the strict rules generally endorsed by the gmat, even though "her" can only refer to jane (since joe is male).
in this case, you'd just have to substitute "jane's" for "her".
that's the way it goes.

in (d), it's technically incorrect to use "they" because there is no place in which both systems are mentioned at once (e.g., with "and").

In D "or rapidly spinning collapsed star" is not a modifier, correct? Therefore does not refer to the "first pulsar" Right?

Ron：you know, i don't really know how you would classify that construction. it probably doesn't count as a modifier, because it doesn't actually modify the noun -- i.e., it doesn't expand upon, restrict, or change the meaning of the noun in any way, as modifiers do.

in any case, regardless of how you may or may not choose to classify it, you should know what this sort of construction (comma + OR + words) does: basically, it provides a definition of the word that comes before it.
e.g.
an own-goal, or goal accidentally scored in one's own net and counting towards the other team's score, is possibly the most embarrassing feat that a soccer player can accomplish.
here, the words following "or" (goal accidentally ... score) are the definition of the term "own-goal".
--
disclaimer:
the above usage is definitely not the only use of "comma + OR"; a much more common use for that construction is as a conventional conjunction, connecting two parallel structures. however, you should know this less common construction, so that you don't immediately mark it as wrong upon seeing it.

'to be sighted' is better for at least two reasons.

(1) 'first NOUN to be VERBed' is generally the preferred form in discussing the results of human efforts/actions/interference/perception/etc., while 'first VERBed NOUN' is generally used to indicate inherent qualities of the noun.
for instance, the following sentence is preferred:
henry bishop was the first musician to be knighted by a british monarch. --> knighting is performed by humans
the following is NOT preferred:
henry bishop was the first knighted musician in britain. --> this makes it seem as though being 'knighted' is an inherent quality with which henry bishop was born, or that he acquired it naturally/accidentally in some other way

(2) the word 'sighted' means 'having the sense of sight', so this sentence also contains the amusing alternative interpretation of referring to a pulsar that can actually see

Choice e：first of all, the word 'discovery' is missing. that's a crucial shift in meaning: it's the discovery, not the pulsar itself, that was 'announced'.
also, the word 'while' - which is sometimes used to indicate contrast - creates a strange ambiguity here: on first reading, it appears to suggest that the announcement (which took place in '68) happened during the summer of '67; this is the usual sense of 'while' occurring in this place in a sentence. (normally, if used to mark contrast, 'while' appears in front of a sentence.)

if 'while' is used for contrast, then it indicates that contrast IN ADDITION TO simultaneity. it's specifically used to describe two contrasting things that are simultaneously true.

yes that's awfully specific, but we can afford that kind of specificity because there are plenty of other contrast transitions (whereas, but, although, even though, yet, etc.) to describe situations that don't fit the 'simultaneity' criterion.

There are 2 problems with A.
- Major problem is "THE other infections." THE is too definitive here, carrying the connotation of "every single one of the other infections."
* THE is also incompatible with "such as":
- Correct: I never read this book, but I read the other books on the shelf.
- Correct: I never read this book, but I read other books on the shelf, such as "Right Hand, Left Hand" and "The Rise and Fall of the Third Reich."
- Incorrect: I never read this book, but I read the other books on the shelf, such as "Right Hand, Left Hand" and "The Rise and Fall of the Third Reich."
- Minor problem is "what they had not..." vs. "something they had not..." The "what" construction is awfully strong, suggesting that this was THE ONE THING they hadn't thought possible.
* As an analogy, compare the meanings of "I want to do what I love for a living" and "I want to do something I love for a living." The first suggests that the speaker has one particular field in mind; the second doesn't.

D：ability只能接to do!
E: an ability 是“dolphins are capable of recognizing themselves in mirrors”的概括性同位语

语义！B选项用that划分出语义层次，不是conducted operations，have greatly downsized，shut down altogether这三项平行，而是have greatly downsized，shut down altogether这两项平行，用that从句划分出去conducted operations

(b) is the best choice here.

(a) is vague because it's overly indirect: the meaning of "investigate changes ... as to their effects" is unclear. what's more, it's probably considered unidiomatic as well, at least in this sort of context.

(b) = correct
the participle "investigating" follows "experiments" immediately. no filler words are necessary; this is good concision.
the wording is clear; there are no awkward double possessives, etc., as in some of the other choices.
"would" is used properly here, as a past-tense form of "will". (i.e., if this sentence were translated into the present tense, it would read "...that changes ... will have")

(c) is ridiculously wordy; there's no way you should give this choice any serious consideration. if you don't realize pretty quickly that this choice is wrong, you should go back and read through a bunch of correct OG answers, trying to internalize the sights and sounds (the "vibe") of the correct answers.

(d) "changes in working conditions' effects" is at best awkward and vague, and at worst ambiguous: the intended meaning is the effects of the changes, but this sentence seems to indicated the effects of the conditions themselves. in other words, a literal reading of this sentence seems to indicate that the conditions themselves haven't changed - only their effects have. that's not the intended meaning of the original.

(e) "what the effects" is ungrammatical.
also, in constructions of this sort, "what" is generally redundant / unnecessary; it's better merely to say "to investigate X" rather than to say "to investigate what X is" (or other such wordy construction).