you eat the correct foods be able to keep fit and stay healthy.
A. Only if … will you
B. Only if … you will
C. Unless … will you
D. Unless … you will
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(答案→)A. Only if … will you
B. Only if … you will
C. Unless … will you
D. Unless … you will
解析：本题考查的是虚拟语气的用法。当only放在句首，修饰状语从句、副词或介词短语时，主句的谓语要部分前置，构成部分倒装。其记妙语是：only位句前，状从、副、介短，部分谓提前。