24. My grandpa has been enjoying good health ever since he _______ smoking.
A
stops
B
stopped
C
has stopped
D
had stopped
本题考查了since的用法。since引导的从句常用一般过去时，主句常用现在完成时。所以答案选B。
根据句意可知，爷爷自从戒烟后身体一直很好。Since后从句常用一般过去时。所以答案选B。
since后从句时态使用错误