Things were very expensive those days.You_______ a very good dinner if you only paid 10.A.can't haveB.may have C.can

2 选B certain
Sure与certain是近义词,均作“一定的,确信的”等解.两者用法相似,多数情况下可换用,但有时不能换用.
在“It is…that结构中只能用certain,不能用sure.例如：
It is certain that he will come.毫无疑问他会来
It was certain that our football team would win the game. 我们的足球队无疑会赢得比赛
如是否定句,用whether,不同that.例如：
It is not certain whether he will come. 他来不来还不一定.
题目疑问句,同理 教授确定还会再来中国吗?
1选C
can/could + have + 过去分词
表示对过去某种情况怀疑或者不确定
can和could一般用于否定句和疑问句,could语气较弱
例句
He can't have finished the work so soon
他不可能这么快完成工作
I didn't see her at the meeting this morning；she can't/couldn't have spoken at the meeting
今天早上我没看到她出席会议,她不可能在会上发过言.
题目 那些日子物价很高,你只花10块钱是不可能吃到什么好东西的