A:Is your grandpa still smoking B:No,it's years since he smoked.这里为什么用since
问题描述：
A:Is your grandpa still smoking B:No,it's years since he smoked.这里为什么用since
答
A：你祖父还吸烟吗?
B：不,他都戒烟几年了.
since he smoked 意为：自他戒烟以来.