B
省略了if 的虚拟语气
如果条件状语从句的谓语动词中含有were, had, should, 可以省略连词if,把were, had, should,放在主语前构成倒装.
本句话本来是：If I should be free tomorrow, I could go with you.
只有should 有这样的用法哦·
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