17. ___B____ I be free tomorrow, I could go with you.

问题描述:

17.   ___B____ I be free tomorrow, I could go with you.
17.   _B____ I be free tomorrow, I could go with you.
A. CouldB. Should C. Might D. Must
为什么不选A呢 谢谢

这是虚拟语气的内容,其实前半句就等于If I should be free tomorrow,然后省略if,把should提前,
在if条件句虚拟中,当跟将来事实相反时,if后面可以用should、were to或直接用动词过去式,但不可以用could,更不可以把它提前