My approach to the correct answer:
The science of economics, which for four decades was
dominated by Keynesian s, who at first stressed the government’s role in stimulating the economy, but who were ultimately led away from solutions based on government intervention.
Error finding: in the original sentence, ",which" introduces a subordinate clause, but main clause "the science of economics" remains incomplete.
So, A is not the answer.
(A) economics, which for four decades was >> reason stated above.
(B) economics that was to be >> "was to be" - wordy
(C) economics, one which has, for four decades, been >> to much unnecessary breakup of sentence.
(D) economics is one that for four decades has been >> Though this sentence has present tense (when remaining sentence has past tense) I chose it because it is clearly conveying the meaning.
(E) economics, for four decades, is one that was >> "is one that was" wordy
1. In a sentence we may have different tenses, but they have to be in different clauses.
2. Too much break up of sentence is unnecessary.
My mantra for cracking GMAT:
Everyone has inborn talent, however those who complement it with hard work we call them 'talented'.
+1 Kudos = Thank You Dear
Are you saying thank you?