_______she couldn’t understand was _______fewer and fewer studentsshowed interest in her lessons．

A.What；why

B.That；what

C.What；because

D.Why；that

答案及解析： A

解析：

主语从句shecouldn’t understand缺少宾语，要用what引导。表语从句fewer and fewer students showed interestin 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”。