They are also worried all the students are able to make good use of the spare time after

问题补充：

They are also worried all the students are able to make good use of the spare time after school.

A. about

B. whether

C. that

D. what

答案：

A. about

(答案→)B. whether

C. that

D. what

解析：本题的含义是他们也担心学生们放学后是否能很好地利用他们的业余时间，whether表示是否的意思，引导一般疑问句，故本题选B。