He to swim when he was five.A. canB. couldC. can be ableD. was able

问题补充：

He to swim when he was five.

A. can

B. could

C. can be able

D. was able

答案：

A. can

B. could

C. can be able

(答案→)D. was able

解析：can和be able to意思接近，不能同时使用，故不选C，can后跟动词原形，故不选AB，故本题选D。