题目
Beardshaw’s did very well _____ the economy was booming, but when a recession came, it saw sales fall dramatically. (A) during (B) for (C) while (C) when
答案是c
我知道while 和 when区别是看后面动词是否加ing,但看到这题我直觉是a
我上网找during 和while差别也觉得答案应该是a (while应该是省略主词)
请问是答案有误，还是我哪里理解错了