Sentence Correction - Verbal and Reasoning

Directions to SolveWhich of phrases given below each sentence should replace the phrase printed inboldtype to make the grammatically correct? If the sentence is correct as it is, mark 'E' as the answer.
Q1:

My doctor knew that I would eventually recover and do kind of work I would be doing before

A would have been doing

B would have done

C had been done

D had been doing

E No correction required

ANS:D - had been doing

No answer description is available.