you eat the correct food be able to keep fit and stay healthy.A. Unless; will youB. Only i

问题补充：

you eat the correct food be able to keep fit and stay healthy.

A. Unless; will you

B. Only if; you will

C. Only if; will you

D. Unless; you will

答案：

A. Unless; will you

B. Only if; you will

(答案→)C. Only if; will you

D. Unless; you will

解析：句意：只有如果你吃了适当的食物你才能保持健康。Only+状语从句放在句首的时候，句子用部分倒装，助动词will放在主语前面，unless“除非，如果不”，不符合句意。选C。