Know your tenses:
Have/has = present perfect (started in the past and continues until now)
Had = past perfect (happened before another event in the past)
1. You need a past tense in order to use the past perfect (I had studied for three years before I took my GMAT).
2. The usage of past and present perfect tenses could work, but again, you need a simple past to say when something started in the past (I had studied for three years before I took my GMAT, but since then I have not wanted to study).
3. The biggest error in the sentence (I have received a high score in GMAT because I had prepared hard for it" is wrong) is meaning: receiving a high score is a one time event (past) not a continuing event (present perfect).
The verb tense in the underlined part of the sentence must be compared with what is taking place now. As the sentence states we have realized that emissions of industrial chloroflorocarbons deplete the ozone layer (present perfect), we need the past perfect had appeared to indicate a time period prior to the present. Additionally, "immune from" means free of exempt from (eg. immune from prosecution), whereas "immune to" means not susceptible (eg. immune to chicken pox). In this case, the ozone layer was considered not susceptible to human influence. Thus, "immune to" is idiomatically correct.
E is too wordy. "appeared immune" is just fine on its own. Notice that we have "it appeared immune." The "it" here refers to the ozone. Thus, to say: "it appeared that it was immune" would be unnecessary.
the best way to process "as varied as" here is as an IDIOMATIC EXPRESSION.
here's a valid way to think about it: you can substitute "including" for "as varied as"; the sentence should still work.
these two don't have exactly the same meaning - i.e., "including" isn't the SAME as "as varied as" - but, if one of them is grammatically ok, then so is the other.
when you have a COMPARISON construction such as the one here ("as varied as..."), it must refer to whatever noun, noun phrase, or other type of construction IMMEDIATELY follows.
you cannot ignore intervening words. so if you have "as varied as those of...", then you must regard "those of..." as the object under comparison.
you'll find this rule pleasant, because it replaces difficult thinking with completely mechanical processes.
There's a very subtle difference in meaning, although the main issue is that of redundancy/wordiness. But consider the difference between these two sentences, which would illustrate the point:
(1) I get mail from cities as far away as Providence.
(2) I get mail from cities that are as far away as Providence.
If I'm in San Francisco, then sentence #2 means, strangely enough, that I get mail from cities that are all exactly 3,082 miles away (the distance from SF to Providence). Sentence #1 implies no such thing.
Similarly, the wrong answer (D) seems to imply that EACH country is somehow as 'varied' as EACH other country. That's not the intended meaning, which is that the SET of countries is varied.
"walker是根据australopithecine的牙齿和chimpanzees and orangutans的相似度来判定它是frugivores的。如果orangutans的饮食结构变了，那说明au也有可能。D选项environment的因素是提出来反对walker不完全对的。walker自己本身并没有考虑到环境。所以walker‘s conclusion不会受到这个影响"
you can't use 'resulting from' as an adverbial modifier, as is done here. in general, 'resulting from' is only used as an adjective modifier, almost always without a comma, as in
the pollution resulting from the chemical spill forced all the local residents to evacuate.
E的逗号没有问题，问题在于decrease in size与后面的l形容词less distinctive， less in demand不能很好地组成平行结构
The problem with choice E is in the placement of the modifier ("For consumers and businesses making a large number of..."). Since this comes before the main clause, "the government predicts...", the implication is that the government is making a prediction for the sake of those consumers and businesses: the prediction is "for" them - and may not even mean that their rates will fall!
Choice A, on the other hand, correctly captures the intended meaning of the sentence: The government is making a general prediction (it's not a prediction aimed at anybody in particular), about the rate cuts that will be experienced by certain individuals.
the passive voice is indeed a problem, because it's unnecessary. (remember that the passive voice should only be employed when there's a fairly compelling reason to use it.) in choice b especially, there's also an unacceptably long distance between the passive-voice action (will be greatly reduced) and the agent of that action (by the ...).
one thing you should definitely notice in choice c is the wordiness of 'the government's prediction is'. constructions like that, which can easily be replaced by more compact forms ('the government predicts') with no change in meaning, are ALWAYS wrong. (also, you need the word 'that' after 'is'.)
the prepositional phrase at the beginning of choice e is an example of a dangling modifier: one isn't quite sure exactly what it's supposed to modify. according to the strict rules followed by the gmat, this phrase should technically modify the action directly following the comma (the government predicts), which doesn't make sense: the government is not making predictions for the benefit of consumers and businesses (rather, it is merely making projections).
choice b "having" + "was ineffective" doesn't make sense.
"having" adopts the same timeframe as the rest of the sentence -- which is the present (we can discern this by noticing that the sentence is talking about patients who do not respond). however, "was ineffective" seems to suggest that the prescription was ineffective sometime in the past.
taken together, these two contexts seem to indicate that the patient is, for some reason, holding onto an old prescription that was ineffective.
choice c would be incorrect because of Parallelism as well. Note that "as" creates a comparison, which is a special case of P-ism. Here the "as" connects "having too low a dosage" with "treatment." The same is the case with E, in a way, as the example give is not an example of a "treatment."
in choice d
1. "It" is ambiguous (original sentence without "It" sounds better)
2. Lack of parallelism "have been" not parallel to "were"
3. "too low a drug dosage" sounds awkwardly at least.
Choice d and e："when" doesn't really work, because the sentence is talking about the things that are actually examples of inappropriate treatment.
Choice a：'the national average' would be exactly what it says: an average.
i.e., some kind of statistic.
it is not a person, so that option is nonsense.
Choice e：we do not have "subject is likely that-clause" in english。
choice a the comparison made in choice a is ok. the real problems with choice a:
- 'the ratio of 42 times' is redundant; it'd be good enough just to say '42 times'. note that the word 'ratio' is not redundant in choices c-d, since it's being used as a modifier to make a logical connection.
- it doesn't say 42 times what. not only is that unacceptably vague, but it also breaks parallelism.
choice b is badly worded: 'compares to 42 times in 1980' seems to say that, on forty-two different occasions in 1980, the ceo:blue-collar ratio reached 419:1. this is not what we are trying to say.
more generally, when speaking about ratios as is done here, you can't just write "42 times" by itself. it has to be 42 times something. sometimes you can use pronouns - the height of the sears tower is more than four times that of the statue of liberty - but you can't use empty space.
choice c exhibits proper usage of 'times' followed by their pay. it also uses the ratio, a correct identification of exactly what is being described.
the construction in choice e doesn't make sense.since that's obviously not the case here——the report points out a fact about these CEOs, not the identities of the CEOs themselves。
* Modifiers like "...(that) they are aware of" are not ok in formal English; you'd want "of which they are aware" (or something totally different, e.g., "that they know") instead.
the person I spoke to --> no; the person to whom I spoke --> yes.
the stores (that) most people shop at --> no; the stores at which most people shop --> yes.
The "no"s here are worth noticing because they are cornerstones of SPOKEN English (i.e., an altogether different language). If English isn't your first language, then avoiding these will, ironically, be much easier than if it were.
"There is / there are..." is just another way of saying that things exist, or that they are in a certain place.
It's certainly not a way of expressing emphasis. As far as the GMAT is concerned, there's no difference between "there are Xs" and "Xs exist", and there's no difference between "there are Xs in this place" and "Xs are in this place".
---- YOU DON'T NEED TO KNOW ANYTHING BELOW THIS LINE FOR THE TEST ----
In terms of the GMAT, as I stated above the line, there's no difference.
In general usage, in fact, the construction without "there is/are" is generally more emphatic.
Mr. Wong, there are two people in your office. --> ok, we're just counting people, presumably for some reason mentioned earlier in the conversation.
Mr. Wong, two people are in your office. --> I specifically want to draw your attention to the people. "They want to see you", or "You should be aware that they're there; maybe you don't want them there."