Your son has kept for two hours. You’d better ask him to have a rest.A. studyB. studiedC.

问题补充：

Your son has kept for two hours. You’d better ask him to have a rest.

A. study

B. studied

C. to study

Dstudying

答案：

A. study

B. studied

C. to study

(答案→)D. studying

解析：keep doing sth表示不断地做某事，故本题选D。