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。
Do you remember all years when scientists argued that smoking would kill us but the doubters insisted that we didn't know for sure?
还记得那些年吗？当初，科学家提出吸烟会导致死亡，而怀疑者们却坚持认为我们还不能确认这一点。
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。
However, we don't know for sure.
然而，我们仍然不能确信。
Well, I don’t know for sure either.
我也不知道。
我们可能永远无法确定。
你怎么能把握得住呢？
您肯定的事情是什么？
你不可能确切知道。
我不能肯定。
Me too. I wish we could know for sure.
我也是。我希望我们能知道得确切些。
That is the only thing we know for sure.
这是我们唯一确定的事情。
But I know for sure that she was my mother's best friend.
可是我知道了，她就是我妈妈的好朋友。
What I know for sure is that what you give comes back to you.
我非常确信一点，就是你付出过什么，你就会有什么回报。
I don't know for sure because I don't look ahead in the scripts.
没提前看剧本所以我也不是很清楚。
But it would be nice to know for sure which directory you're now in.
但确定您现在所处的目录还是不错的。
We can't know for sure because this is not a controlled experiment.
我们不能确定，因为这不是一个可控实验。
Sal: Hard to know for sure, but we believe in aloha 'aina: love of the land.
赛儿：确实很难讲，但是我们相信阿啰哈爱纳：对土地的热爱。
We all desperately want to get it right and never know for sure whether we are.
我们都拼命的想做对的事却永远不确定我们做的到底对不对。
Do you know for sure that there aren't any memory leaks in your running services?
你能肯定的知道正在运行的服务里面没有内存泄露吗？
Once you've got a potential candidate, how will you know for sure they can do the job?
一旦你已经有了一个潜在的候选人，您将如何确切知道他可以做好工作呢？
Don't buy your textbooks until you know for sure the teacher is actually going to use them.
不要买教科书，除非你确信你的导师会用到它们。
Maybe it'll never be right for your company, but you won't know for sure without giving it a try.
也许它永远都不会适合于您的公司，但是，如果不尝试一下，您就不会确切地知道这一点。
But the study results were not conclusive, and more research is needed before we know for sure.
但是研究结果并非盖棺定论，在我们确切明白之前还需要做更多的研究。
I'll never know for sure, because both stress and certain antidepressants can cause hair loss.
我无法知道确切的原因。因为压力和某些抗抑郁药物均可能引起脱发。
I'll never know for sure, because both stress and certain antidepressants can cause hair loss.
我无法知道确切的原因。因为压力和某些抗抑郁药物均可能引起脱发。
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