If I you I the army.A am would join B. were would join C am will join D. were will

问题补充：

If I you, I the army.

A, am, would join B. were ,would join

C am, will join D. were ,will join

答案：

解析：虚拟语气是一种特殊的动词形式，用来表示说话人所说的话并不是事实，而是一种假设、愿望、怀疑或推测。其主要有三种结构：

1、与现在事实相反

若与现在事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”

2、与过去事实相反

若与过去事实相反，条件从句的谓语用过去完成时(had+过去分词)，主句谓语用“should (would, could, might)+have+过去分词”

3、与将来事实相反

若与将来事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”。

句意：如果我是你，我会加入军队。结合语境可知本句描述的是与现状相反的事实，故选B。