He makes occasional visits to Delhi.

The correct answer is C. regular.

The word “occasional” means “happening from

time to time, but not often.” The word “accidental” means “happening by chance.” The word “strange” means “unusual or surprising.” The word “frivolous” means “not serious or important.”

In this case, the man makes occasional visits to Delhi. This means that he visits Delhi from time to time, but not often. This is a regular occurrence, not an accidental or strange one. It is also a serious and important matter, not a frivolous one.

Therefore, the correct answer is C. regular.