Sentence Improvement - Verbal and Reasoning

Directions to SolveIn questions given below, a part of the sentence isitalicised and underlined. Below are given alternatives to the italicised part which may improve the sentence. Choose the correct alternative. In case no improvement is needed, option 'D' is the answer.
Q1:

No sooner he had returned home then his mother felt happy.

A had he returned home when

B he had returned home than

C did he return home than

D No improvement

ANS:C - did he return home than

No answer description is available.