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:

They should have calmly thought of the advantages that would accrue to them.

A should have been calm in thinking about

B should be calmly thought of

C shall have to calmly thought of

D should have calmly think of

E No correction required

ANS:E - No correction required

No answer description is available.