求各位大神一道英语题，就是我很笨啦，麻烦讲详细点，一定要详细点，谢谢了~

这道题选A，考察certain和sure的用法差异。

It is…that 结构中只能用 certain，不能用 sure。 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。其用法区别大致如下：
一、 两者可换用的情况：
1． 跟不定式，可用人或物作主语。例如： It is sure/certain to rain. He is sure/certain to come. You’re sure/certain to be happy with them.
2．跟连接代/副词引起的不定式，常用人作主语。例如： I’m not sure/certain what to do. He was not sure/certain when to start.
3．跟 of 或 about 引起的短语。sure 后可跟 of doing sth. 常用人作主语。
例如： I’m not sure/certain of that. Are you sure/certain about it? I’m sure of his coming. He’s sure of winning.
注：sure to do sth.与 sure of doing sth.的区别：前者表示说话者认为“主语一定…”；后者表示 “主语自认为一定…”。
例如： He is sure to succeed. (说话者认为“他”一定会成功。 He is sure of succeeding. (“他”自己认为一定成功)
4．跟 that 引起的从句，常用人作主语。例如： I’m sure/certain that he’ll come. I was sure/certain (that) he had seen me. I’m quite sure/certain I left the book on the table. 注：当 sure 或 certain 用于否定句时，其后跟 whether 或连接代/副词引起的从句，不跟 that 引起的从句。例如： I’m not sure/certain whether I’ve met him before. I’m not sure/certain whether he will come. I’m not sure/certain who he is. I was not sure/certain what I ought to do. I’m not sure/certain why he wants it. 以上几种情况中的 sure 与 certain 虽可换用， 但隐含意思不同。 Sure 表示主观的推测或感觉， 所述事实并不一定如此；certain 则指说话者有充分的理由或根据，肯定某事会发生。如下面 两句中的 certain 均不可用 sure 替换。例如： I’m certain he wasn’t in the classroom. I saw him in the library. I’m certain than he will go the concert. He told me so an hour ago.
5．与 make 连用构成短语，后跟从句，作“弄清楚；设法做到”解。例如： Make sure/certain when the train leaves. Have you made sure/certain that the train has already left?
6．与 for 连用构成短语，在句中作状语。作“确实；毫无疑问”解。例如：I don’t know for sure/certain that he’s dead. I cannot sau for sure/certain when he will come.
二、 两者不可换用的情况：
1． 在“It is…that 结构中只能用 certain，不能用 sure。例如： It is certain that he will come. It was certain that our football team would win the game. 如是否定句，用 whether，不同 that。例如： It is not certain whether he will come.
2． 在祈使句中通常用 sure，不用 certain。例如： Be sure to tell me all the news. Be sure and come as soon as possible. Be sure you don’t upset any of them.
3．作定语时，sure 作“有把握的；肯定的；可靠的”解；certain 作“某个；某些”解。如： Put it in a sure place. There was only one sure way to succeed. A certain person called on me yesterday. Certain students have failed in the exam.
4．Sure 在美语中可用作副词作肯定答语，用以代替 surely，相当于 certainly，of course；而 certain 则不能用作副词。
如： I wonder if I could use your phone. Sure. Go ahead. Zhou Lan, can I have a look at your copy of China Daily? Sure, go ahead.

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