In a review of 2000 studies of human behavior that date back

In a review of 2000 studies of human behavior that date back to the 1940's, two Swiss psychologists, declaring that since most of the studies had failed to control for such variables as social class and family size, none could be taken seriously.


(A) psychologists, declaring that since most of the studies had failed to control for such variables as social class and family size,

(B) psychologists, declaring that most of the studies failed in not controlling for such variables like social class and family size, and

(C) psychologists declared that since most of the studies, having failed to control for such variables as social class and family size,

(D) psychologists declared that since most of the studies fail in controlling for such variables like social class and family size,

(E) psychologists declared that since most of the studies had failed to control for variables such as social class and family size,

Here it goes:

The medium-length underline contains two commas, signaling likely Structure, Modifier, or Meaning issues.

Issues

(1) Structure

Like many GMAT sentences, this one begins with an opening modifier, followed by the subject of the sentence, two
psychologists, and then another modifier, declaring that. What verb goes with the subject?

Although the modifier declaring that…size is not incorrect because it could potentially modify psychologists, a modifier
cannot contain the sentence's main verb, so it can't help with the missing verb problem. The next and final chunk of the
sentence, none could be taken seriously, is a complete clause on its own and does not contain a verb for psychologists.
Answer (A) is just a sentence fragment.

Answer (B) is similar. It adds an and to the final clause, but the sentence still has no main verb to go with the subject
psychologists. Eliminate answers (A) and (B).

Answers (C), (D), and (E) fix the missing verb problem by changing the modifier declaring into a main verb form: declared.
Answer (C) creates another missing verb problem, though: most of the studies is also a subject that needs a verb but answer
(C) replaces the verb failed with the modifier having failed. Eliminate answer (C).

(2) Verb: fail

Scan the answers and note that there are three variations in verb tense: had failed, failed, and fail. When did the studies fail?

The full clause states that since the studies fail / failed / had failed, none could be taken seriously. The verb form could be is
either indicating a past tense or a polite statement or request (Could you please do this for me?). In this sentence, could be is
indicating a past time frame, so fail shouldn't be in the present tense. Eliminate answer (D).

Answers (A), (B), and (E) all use acceptable past tenses; answer (C) changes the structure (see the discussion of Structure for
more).

(3) Idiom: failed in controlling

The answers contain a split between failed in controlling in answers (B) and (D) and failed to control in answers (A), (C),
and (E). Are both versions acceptable?

Try some simpler examples:
She failed to control her temper.
She failed in controlling her temper.

The first example is the correct idiom; the second is incorrect. If some action is what failed to happen, use the infinitive form (in this case, to control) rather than the gerund form as the object of a preposition (in this case, in controlling). Eliminate answers (B) and (D).

(4) Comparison: such X like Y

Towards the end of the underlined section, there is a split between such variables as social class and such variables like
social class.

The word like means “similar to.” This sentence is trying to introduce examples of something; the correct idiom for introducing
examples is such as. Eliminate answers (B) and (D).

Correct answer (E) contains a subject and a verb for both psychologists and most of the studies. It also uses the correct idiom,
such as, to provide an example.