We have appealed to him again and again, there is no use flogging a dead horse now.

Options

A. repeating our request
B. making him see reason
C. beating about the bush
D. wasting time in useless effort

Answer

D

Explanation

flogging a dead horse: wasting your effort by trying to do something that is no longer possible He was warned again and again, but now I think there is no use flogging a dead horse. The best option is wasting time in useful effort.