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:

He should move on to the next point, and not harp one sting only.

A harp on string only

B harp only one string

C harp upon one string only

D No improvement

ANS:C - harp upon one string only

No answer description is available.