问题补充：
Tom’s teacher kept on telling him to practise speaking English, but didn’t work.
A. he
B. which
C. all
D. it
答案：
A. he
B. which
C. all
(答案→)D. it
解析：but 后句子少主语，而主语恰巧是Tom’s teacher kept on telling him to practise speaking English这件事，it 可代替前一句。故选D
