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:

I would have waited for you at the station if I knew that you would come.

A had known

B was knowing

C have known

D No improvement

ANS:A - had known

No answer description is available.