in any case, all three of the following are legitimate:
evidence to suggest...
evidence that suggests...
evidence suggesting...
you will never have to choose between two choices that are fully correct; if you see 2 legitimate versions of some idiom, then something will be wrong elsewhere in one of the choices.
"has descended" means "has moved downward". this can be in either a literal sense (he has descended to sea level from a height of 8000 feet) or a metaphorical sense (i don't want to descend to the level of common street thugs), but it can't refer to ancestry.
if you mean to discuss ancestry, which is clearly the case here, then you must use "is descended".
"is descended from" is indeed a description of a condition in the present. it's the same thing as "is a descendant of".
e.g. my friend is a direct descendant of George Washington.
you wouldn't say "was", unless my friend is dead.
same thing with the elephant - if you write "the elephant was..." in this case, you are actually implying that the elephant is extinct.
B：
- sentence fragment (there's no main subject, and/or no main verb: the whole thing is one big whether X or Y construction, which can't stand alone as a sentence)
- 'whether or not' is wordy (yes, that's enough to kill this answer choice all by itself) on the GMAT, whether or not is considered redundant.
Eliminate B, C and E.
- change in meaning: the way this is written, it's the status quo that is affecting the U.S., whereas the sentence is supposed to say that the decision (whether Taiwan will do blah blah blah) is what will affect the U.S.
D:
- the pronoun 'it' doesn't have an antecedent. there are certain idiomatic constructions in which a standalone 'it' is allowed (such as 'make it difficult to...'), but this isn't one of them.
- bad parallelism: 'will develop' is in the future tense, but 'preserves' is in the present tense. as they are alternatives in a decision, these must be presented in the same tense.
If whether is used to connect two verbs/actions, I'd keep it simple and just analyze all such situations with "or" as the parallel marker.
--
If whether is used to connect two nouns, THEN I'd consider both "whether" and "or" as parallel markers.
E.g., Everyone in the country, whether civilian or soldier, was in danger during the war.
(A) I can’t complain about this one. “Carbon dioxide gas” is a singular, non-countable noun, so “less” works fine as a modifier. And this part is a little bit tricky, but the second part of the sentence refers to several different “gasses” – a countable, plural noun – so “fewer” is appropriate.
The phrase beginning with “that” (“that have been implicated…”) correctly modifies “other gasses.” It’s also completely fine to use the “-ing” form of the verb after “as well as.”
So we’ll keep (A).
(B) It’s a funny quirk of English: if “as well as” were changed to “and” then we’d want the verbs “burn” and “emit” to be in parallel form. But since we have “as well as”, we’re better off using “emitting”, as we did in (A).
More importantly, I can’t make any sense of the “having been” at the end of the underlined portion. For that reason, we can scrap (B).
(C) You could argue that the pronoun “they” is ambiguous here, since it could refer to “diesel engines” or “gasoline engines”, but I’m not convinced: since “they” is the subject of the second clause, it can generally refer back to the subject of the first clause on the GMAT without causing any trouble.
But we definitely have a modifier problem here: “fewer carbon dioxide” doesn’t make any sense, since “carbon dioxide” is a non-countable noun, and “fewer” can only be used with countable nouns. (If you’re not clear about that concept, try counting the noun out loud: “one carbon dioxide, two carbon dioxides, three carbon dioxides…” That makes no sense at all, right? So “carbon dioxide” is non-countable.)
(D) The first part of the underlined portion isn’t necessarily WRONG, but it definitely isn’t great: “gasoline engines that have a comparable size” is a really crappy way to say “gasoline engines of comparable size.” I just don’t think it makes sense to use the word “have” in this context, since gasoline engines don’t really possess size.
More importantly, we have a problem with the non-countable modifier “less”, since it seems to be modifying both “carbon dioxide gas” (non-countable) and “other gasses” (countable) – and “less” can’t modify a countable noun.
(E) The first part of the underlined portion suffers from the same problem as (D): “that have a comparable size” is a lousy way to say “of comparable size.” But again, I wouldn’t necessarily eliminate (E) based on that issue by itself.
The other problem is the same as in (D): “less” seems to modify “other gasses”, and that doesn’t work. Plus, I’m really not sold on the idea of using “having” to modify “gasses” at the end of the underlined portion – the version in (A) (“gasses that have…”) seems a little bit better.
比较的题型：1）比两样东西（名词），2）比两个动作（动词）。
这里比较的是两个动作，所以，有一个省略用法 [sub+verb]+modifier，只保留modifier，选C。
如果是比较两个东西, 比如circulation in.... is lower than that in ....，就应该是D。
（newspaper）{had} 《lower circulation》 in the six months than（newspaper）{ had} in a similar period
改写为两个东西比较：the circulation of newspaper in the six months is lower than that in a similar period
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.
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in any case, all three of the following are legitimate:
evidence to suggest...
evidence that suggests...
evidence suggesting...
you will never have to choose between two choices that are fully correct; if you see 2 legitimate versions of some idiom, then something will be wrong elsewhere in one of the choices.