（中学） 情态动词问题It's nearly 7 o'clock.Jack ___be here at any moment.A.mustB.needC.shouldD.can但为什么不能用can啊?With so much work on hand,you___ to see the game last night.A.mustn't goB.shouldn't goC.couldn't have goneD.shouldn't have gone但为什么不是couldn't?表对过去的猜测

It's nearly 7 o'clock. Jack ___be here at any moment.
A.must
B.need
C.should
D.can
答案是C，但为什么不能用can啊？---should(应该)at any moment（随时），而can用于表推测一般用于“否定句”和“疑问句”中。
With so much work on hand, you___ to see the game last night.
A.mustn't go
B.shouldn't go
C.couldn't have gone
D.shouldn't have gone
答案是D，但为什么不是couldn't? 表对过去的猜测----shouldn't have done sth.表示本不该做的事实际上却做了；而couldn't have done sth表示本不可能做某事却做了
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解决第一题,
你可以看到,句意是说jack本应该来应该在这,但是现在却不在.should有这个意思.而can是表示jack能在这
第二题是这样的.
仔细看题干,他的意思是,你不应该去看比赛.但是事实上已经去看了比赛.
有个固定句型：
shouldn't have done 表示本不应该做而做了.