One should keep one's promise.
A. One's promise should be kept.
B. One's promise has to be kept.
C. A promise should be keeping.
D. A promise should be kept.
Answer: Option A
Solution (By Examveda Team)
One's promise should be kept.The subject 'One' has to be replaced with 'One's promises' keeping the tense same.

I think the correct answer is "A promise should be kept."
My uncle is not as clever as my father . (Change into comparative degree)