问题
选择题
Your son has kept _______ for two hours. You'd better ask him to have a rest. [ ]
A. study
B. studied
C. to study
D. studying
答案
答案：D
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Your son has kept _______ for two hours. You'd better ask him to have a rest. [ ]
A. study
B. studied
C. to study
D. studying
答案：D