前面even if they can并不需要虚拟，因为是事实。所以不能用could afford。【真实条件句，不能用虚拟】
后半句的意思是“假如这些家电放在以前，祖父母会觉得很神奇”，事实上这些家电放在以前是绝对不会发生的情况，所以用past perfect 。【非真实条件句，要用虚拟】
混合虚拟语气！各用各的，所以这样组合是可以的。
2. 平行触发语rather than/instead of (!)
rather than后面的动词可以是-ing形式，也可以是省略to的不定式形式，即rather than doing或rather than (to) do。
rather than前后的动词形式要保持一致，前面是doing形式则后面也用doing形式，前面是to do形式则后面也用(to) do形式（to可以省略）。
但rather than位于句首时，则只能接不带to 的不定式。比如Rather than throw away the leftovers, John stored it in the refrigerator. 约翰没有扔掉剩菜，而是把它放在冰箱里。
(d) and (e) contain a COMMA + -ING modifier that is used incorrectly.
a COMMA + -ING modifier is an adverbial modifier that modifies the entire clause to which it's attached, and is attributed to the subject of that clause.
in this context, you only want to modify the preceding noun ("tribes"), so COMMA + -ING is inappropriate.
2 idiom errors in (b):
* "interact" MUST be paired with "with". "interact between" and "interact among" are unidiomatic.
* "among each other" is unidiomatic (as is "between each other"); you should write "among themselves" or "between themselves". but, again, this doesn't work with "interact" anyway, so the issue is moot here.
Answer A suggests that the manufacturers are making small cars efficient, i.e. they're changing small cars, but in fact they're making small cars that are efficient.
I don't think that pronoun ambiguity is the criterion here.
the sentence is supposed to say that today's small cars are more fuel-efficient than previous small cars -- i.e., OTHER small cars.
this is important, because you can't use a "they"/"their" construction (which would illogically imply that you're talking about the same small cars mentioned in the first part of the sentence).
the use of "those" in (c), on the other hand, accomplishes this distinction nicely.
analogy:
sprinters in texas can run faster than they can in north dakota.
--> illogical; in this sentence, "they" would be taken to mean "sprinters in texas" (i.e., not just sprinters).
sprinters in texas can run faster than those in north dakota.
--> makes sense; "those" = sprinters, in this case.
same thing with "they/their" vs. "those" in these instances.
In general, the point of "that" and "those" is to stand for nouns without any attached modifiers/descriptions.
There's an explicit contrast with "it" and "they", which stand for a noun with all of the attached modifiers.
E.g.,
The government of Country X is more stable than it was two years ago.
"It" = "the government of country X"
It is impossible to use "it" to stand for government in general. In this context, "it" can refer only to the government of country X.
Vs.
The government of Country X is more stable than that of Country Y.
"That" = "the government". NOT the government of country X.
The whole point of comparisons, of course, is to compare two different things. So, these pronouns are extremely useful because they're designed to do exactly that-- to stand for only the parts that are actually the same.
establishing the intended meaning is ALWAYS the FIRST STEP of ANY sentence correction problem!
without the intended meaning, most splits are actually impossible to decide, since the vast majority of grammar rules just serve to specify the meaning of whatever construction.
B and D - Incorrect because they do not include the "he" in the end. Without this subject, the rest of the sentence doesn't make much sense.
C - Incorrect because the primary clause is just a fragment:
* Remove the parenthetical phrases "even though...telescope", and "in 1609" and you will see that C is missing a verb as it reads: "Gallileo on hearing that such an optical instrument had been made, he quickly built his own"
E - Incorrect because of the double negative "Even though...but when he heard". Double negatives are a no-no on the test.
C, D, and E - Incorrect because "even though" is not appropriate in this case as it isn't consistent with the intended meaning of the sentence. "Even though" should be used to show mitigating circumstances, or to introduce a paradox as in the examples below:
it's an adverbial modifier that modifies the action of the clause with which it's associated. technically, that action is encapsulated by "is (able)", although it's probably easier to think of it as "modifying the entire clause".
with modifiers that serve as adjectives (such as "..., which ..."), it's crucial that you isolate the single noun modified by the modifier.
on the other hand, with adverbial modifiers, it's unimportant to isolate the single word being modified, because the placement of the modifier isn't restricted anywhere near as severely as with adjective-type modifiers.
as stated above, "dependent" is an adjective, modifies the tree. "depending" is a participle (which introduces an adverbial modifier that modifies the action of the clause, rather than modifying a noun).
the problem lies in the different meanings of the 2 words. "dependent" refers to reliance on another for some kind of support (as in "my children are dependent on me for their food and shelter"). so not only is that choice sketchy in terms of grammar, but its meaning is also all kinds of wrong: it makes no sense to say that a tree is "dependent" on its size (does its size provide it with food or water? etc)
when you see this sort of thing tested, this is all you generally need to do:
* find the second part of the comparison (after the signal)
* figure out what the first thing should be (to create parallelism)
* see if it's there
E:
the second thing (after 'as') is for her skillful wax renderings of popular public figures.
for + THING
...so the first thing should be for her eccentric personality.
this exact construction is there.
B:
the second thing (after 'as') is for skillful wax renderings of popular public figures.
for + THING
...so the first thing should be for her eccentric personality.
this isn't there. instead we have "for + verbING".
Ron：
choice a: bad parallelism
because of... is not parallel to for...
choice b exhibits poor parallelism:
having an eccentric personality is placed in parallel with skilful wax renderings....
choice c: extremely bad parallelism
- one part is a phrase (because of ...), and the other part is a complete clause (she was for her ...)
- same issue as choice a, because vs. for
choice d: bad parallelism
- you can't get rid of the 'for' in the second part (it should be '...as for having...')
- wordy (compare with the compact wording in choice e)
choice e exhibits proper parallelism, in that both of the parallel items are noun phrases (the principal nouns being personality and renderings).
there are two splits you should use to narrow down this problem:
(1) the second half of the construction 'ten times as much ... ____' is as, not than. therefore, you can eliminate answers (a) and (e), which contain 'than'. (i'm assuming that (e) is supposed to say 'than', not 'then'; i don't think the gmat problems would that blatant an error)
(2) the pronoun 'it' is inappropriate, because 'it' must refer to the ENTIRETY of the noun phrase serving as an antecedent.
for instance, the following is an improper sentence: last year's attendance was ten thousand greater than it was this year
in the above sentence, the pronoun 'it' must necessarily refer to last year's attendance, not just attendance.
the problem in this post has the same issue: the pronoun 'it' must refer to more than ten times as much energy, not just energy - an interpretation that makes no logical sense. therefore, all answer choices containing the pronoun 'it' are wrong.
if you don't like '...than was the case', you should learn to like it; this is one of those phrases that the gmat writers use to refer to concepts that don't fit under the usage constraints of traditional pronouns. (another popular one of these constructions is 'do so'.)
The PAST tense is used for:
* HISTORICAL ACTIONS
Ex: Mexico achieved independence in 1810.
* POINT ACTIONS that do not have a direct bearing on the current situation
Ex: Thomas, who is the president of First National Bank, won two Olympic medals in track
and field.
* ENDURING ACTIONS/STATES that are FINISHED
Andrea was the president of First National Bank from 1990 to 1994.
--
The PRESENT PERFECT is used for:
* POINT ACTIONS that DO have a direct bearing on the current situation
EX: Thomas, who is the fastest sprinter in his country’s history, has won two Olympic medals
in track and field.
* ENDURING ACTIONS/STATES that are STILL ONGOING
Carlos has been the president of First National Bank since 2001.
Note that, in some cases, the same point action could be described either by the past tense or by the present perfect tense!
(See the two examples with "Thomas" above.)
When a sentence opens with "In xxxx", followed by a comma, that modifier describes the entire action of the sentence.
In my house, children wear respectable clothes.
--> This is a general statement about the dress code at my house: If children are there, they dress respectably.
It's not a statement about any child(ren) that are actually at my house right now.
If "in xxxx" follows a noun, without a comma, then it describes the noun.
The children in my house wear respectable clothes.
--> There are children in my house right now; this sentence describes their sartorial habits. (This sentence implies nothing about what generally happens in my house.)
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X is second only to Y = only Y can be better than X out of all the options available 排序必定是 No.1 Y No.2 X .....X is only second to Y = X is second to Y, but may be first, third, or tenth compared to other options available No. a 是 Y No.a+1 X