问题补充：
she couldn’t understand wasfewer and fewer students showed interest in her lessons.
A. What；why
B. That;what
C. What；because
D. Why；that
答案：
(答案→)A. What；why
B. That;what
C. What；because
D. Why；that
解析：主语从句she couldn’t understand缺少宾语,要用what引导。表语从句“fewer and fewer students showed interest in her lessons”是一个完整的句子,要用why引导,意思是“为什么越来越少的学生对她的课感兴趣”。
