语法综合练习7
问题描述：
语法综合练习7
Sales of CD's have greatly increased since the early 1990s,when
people ______ to enjoy the advantage of this new technology.
A.begin B.began C.have begun D.had begun
请详细写出解题的过程和思路.
答
选B,1990s就是一个过去时间概念,由when来引导,所以这里直接用过去时.