. The boy was sitting at the desk hard when his mother got home. A. to pretend to workB.

问题补充：

. The boy was sitting at the desk, hard when his mother got home.

A. to pretend to work

B. to pretend to be working

C. pretending to work

D. pretending to be working

答案：

A. to pretend to work

B. to pretend to be working

C. pretending to work

(答案→)D. pretending to be working

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