Father asked Latha the reason for the many questions she was asking. Latha exclaimed good-humouredly that in event of not knowing the answer one should .

These are the options for the question :Father asked Latha the reason for the many questions she was asking. Latha exclaimed good-humouredly that in event of not knowing the answer one should.

A. keep asking till one does.
B. kept asking till one does.
C. keep asking till one do.
D. kept on to ask till one do.

The correct answer is :A. keep asking till one does.