'I must be crazy,' she thought.

“我准是疯了。”她想。

《牛津词典》

She must be crazy to lend him money.

她把钱借给他，一定是疯了。

《牛津词典》

You must be crazy!

你一定是疯了！

youdao

to be talking about how he must be so crazy and weird and everything, and

在谈论说他一定很疯狂，很怪异等等，

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And if you really think they are not building a Smash Bros follow up you must be crazy.

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He thought they must be crazy even though it was true.

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Or they must be crazy.

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