Doctors say that exercise is important for health but it be regular exercise. A. canB. w

问题补充：

Doctors say that exercise is important for health, but it be regular exercise.

A. can

B. will

C. must

D. may

答案：

A. can

B. will

(答案→)C. must

D. may

解析：考查情态动词：A. can能 B. will将会C. must 必须D. may可以，句意：医生说，锻炼对健康很重要，但一定要是定期锻炼。选C。