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,
1. Subject psychologists needs a main verb and gerund (declaring)cannot be a main verb.so use of verb declared is correct.
so A & B is out.
2.In choice C: having failed is a participial form and as such cannot be the main verb in the clause.also it looks very awkward.so choice is also out.
3.In choice D: English has a rule of sequence of tenses:
once a verb form is marked for past tense,the following verb forms that describe the same object or event have to be in the past tense as well. Thus,fail is the wrong verb form. The expression such X like Y is incorrect in English; the correct usage is such X as Y.
by this reason D is also out.
so we are left with correct choice E.
however one can argue why past perfect is used in choice E?where are the sequence of event? and this may confuse some one whether this is the correct choice!!
here is explanation for past perfect "had failed" is correctly used :
All the events in the statement:
1. Psychologists declared
2. Studies failed
3. Could not be taken seriously
Are all of these three events independent?
The answer is No.
The first event i.e. declaration is independent because the act of declaring is not dependent on what was declared.
However, the failure of studies and taking them seriously are dependent. The failure of studies to control for variables must precede the event - they cannot be taken seriously. Isn?t it?
Can we say that both the second and the third events take place simultaneously? It means saying that studies failed to control for variables and at the same time, they could not be taken seriously.
No. The second event must precede third event. Why? The reason is that the second event explains the third event. First, the studies failed. And because it failed, it could not be taken seriously.
So to express this sequence that first the studies failed and then they could be taken seriously, past perfect tense is used for the event that took place earlier.
kudos if you like!!