827. The science of economics, which for four decades was dominated by Keynesians, who at first stressed the government’s role in stimulating the economy, but who were ultimately led away from solutions based on government intervention.

(A) economics, which for four decades was
(B) economics that was to be
(C) economics, one which has, for four decades, been
(D) economics is one that for four decades has been
(E) economics, for four decades, is one that was

Solution:

Tenses + Subject-verb Agreement

A, B, and C, are incorrect because the independent clause (“The science of economics…”) lacks the primary verb.
E is incorrect because of the use of past tense. Present perfect tense is required here.
In D, the primary verb “is” completes the independent clause and hence, D is the right choice.

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