No one knows for sure what happened.

谁也不知道究竟发生了什么事。

《牛津词典》

No one knows for sure why adolescence is unique to humans.

没人确切知道为什么青春期是人类独有的。

《柯林斯英汉双解大词典》

No one knows for sure when or why it began to symbolize peace.

没有人确切地知道它是什么时候或者为什么开始成为和平的象征。

youdao

No one knows for sure who gave it this name in the eighteen thirties.

VOA: special.2010.03.21

While analysts say no one knows for sure how many jobs the stimulus has created, President Obama says he's under no illusions that one program alone can solve the nation's economic problems.

VOA: standard.2010.06.18

No one knows for sure what would happen if there were no resolution by then.

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And no one knows for sure -- not even the dueling Upper West Side mothers.

CNN: Should babies be allowed to 'cry it out'?

Whether the bank is the next target of Wikileaks, no one knows for sure.

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