We don't know for sure how much mass our Sun's lost over the last four billion years.

我们不知道我们的太阳在过去的40亿年里损失了多少质量。

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Scientists are continually learning more about sleep, but one thing they know for sure is this—for humans, it is as important as food and water.

科学家正在不断加深对睡眠的研究，他们对其中的一件事实确信无疑：对于人类来说，睡眠与食物和水一样重要。

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We'd probably know for sure whether someone was shooting at the president from that famous grassy knoll.

我们可能确定是否有人正在从那个著名的草地山丘草地上向总统射击。

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Experts do not know for sure about his mother,Caterina.

VOA: special.2010.09.15

It's been disputed and one doesn't know for sure.

尽管这点还存在争议。

耶鲁公开课 - 文学理论导论课程节选

it's Shopbot for people, you know, make sure things sell,

对人们来说，那就是个比价器，确保东西卖得出去，

在布鲁明戴尔百货 - SpeakingMax英语口语达人

We do know for sure by now that was the right way to create jobs.

FORBES: How to Create Jobs: Stop Misguiding the Animal Spirits of Entrepreneurs!

Hard to know for sure, given that the SBA keeps track of the figures.

FORBES

We know for sure that there are differences between the male and female brain.

BBC: Art appreciation 'a gender issue'