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
网友回答
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。