1.Ican't believe it.意为“不会吧”“怎么可能”“不敢相信”
Eg.Oh,my God! This is so cool! I can'tbelieve it!
天啊！太帅了！怎么可能这么帅！
Eg.Oh,my gosh! I can'tbelieve it! We're roommates!
我的天！真不敢相信！我们居然成了室友！

2.Believeme.是“相信我”“真的”的意思，与youreally should believe me同义。believeme when I say...是“要相信我说的……”的意思。
Eg.Believe me, your feelings are just asimportant as hers.
相信我，你的感情和她的感情一样重要。
Eg.Believe me when I say I triedto calm her down.
相信我，我试图让她冷静下来。

3.youhad better believe it是“你最好还是相信”的意思，也就是“错不了”“真的”的意思。you better believe that..也是“……是朕的”“……没错”的意思。可以省略had或you.
Eg.You better believe it, lady.
女士，这是真的。
Eg.You better believe he'stired, after the day we had!
忙了一天了，你最好相信他是真的累了！

4.expectsb. to believe...是“让……相信……”的意思。
Eg.You can't expect me to believe that.
你别指望我去相信那些不像话的事情。
Eg.Youexpect me to believe that nothing happened?
你让我相信什么事情都没有发生？