People may not be sure about life on Mars until a sample of life is brought back.

人们可能不确定火星上是否有生命，直到一个生命样本被带了回来。

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Even now we could not be sure that the militants would not find some new excuse to call a strike the following winter.

即使到现在，我们也不能确定这些激进分子不会找到某个新的借口在下一年冬天号召一场罢工。

《柯林斯英汉双解大词典》

One thing is for sure —it's not going to be easy.

有一点可以肯定—事情不会很容易。

《牛津词典》

They want to be sure that he is not dealing off the bottom of the stack of cards.

VOA: special.2009.11.22

I'm not at all sure there's anything more to be said about that passage, which I think lays it to rest.

我不确定这篇文章是不是,还要更多的讲解，就这样的吧。

耶鲁公开课 - 文学理论导论课程节选

You just got to be looking around all the time to make sure you are not going to be run down.

你随时观察四周以确保你不会被撞倒。

伦敦的蓝色自行车 - SpeakingMax英语口语达人

Even though your idea may be untested and you may not be absolutely sure of your business model, try it.

FORBES: Face your Fears: The Spy Games Story

Notably, in the case of North Lakelands NHS Trust the CHI team concluded that it could not be sure that the problems of abuse of patients and failure to act on complaints would not be repeated.

BBC: NHS inspectorate shows its teeth

He said he believed everyone had been accounted for but could not be sure.

BBC: Colorado Loveland avalanche kills five snowboarders