问题描述：
一道有关情态动词的英语选择题
---When can Ifetch my clothes?I need them this evening.
---They ____ be ready by 4 o'clock.
A.can B.should
答案选的是B.
求教：为什么不能选A?
---When can Ifetch my clothes?I need them this evening.
---They ____ be ready by 4 o'clock.
A.can B.should
答案选的是B.
求教：为什么不能选A?
问题解答：
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