you take an active part in physical activity be able to keep fit and stay healthy.A. Onl

问题补充：

you take an active part in physical activity be able to keep fit and stay healthy.

A. Only if; you will

B. Only if; will you

C. Unless; you will

D. Unless; will you

答案：

A. Only if; you will

(答案→)B. Only if; will you

C. Unless; you will

D. Unless; will you

解析：考查倒装句：句意：只有你积极的参加体育活动，你才能保持健康。Only后面接状语从句的时候，主句应该用部分倒装，助动词will放在主语前面，选B。