Do you think exercise can keep us ？A. well　　　B. good　　　C. fit　　　D. fine

问题补充：

Do you think exercise can keep us ？

A. well

B. good

C. fit

D. fine

答案：

A. well

B. good

(答案→)C. fit

D. fine

解析：句意：你认为运动能让我们保持健康吗？keep fit是固定用法，意思是保持健康，选C。