Completing all the homework by the dinner John felt very tired. He all day long.A. was st

问题补充：

Completing all the homework by the dinner, John felt very tired. He all day long.

A. was studying

B. studies

C. has studied

D. had been studying

答案：

A. was studying

B. studies

C. has studied

(答案→)D. had been studying

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