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。
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。
Alex rooms with Henry Thorpe, and since Henry is one of the senior prefects, he would know for sure.
阿列克斯和亨利·骚伯同屋，而亨利是四年级级长之一，他准知道。
'Whether anything fell to Earth or not, we won't know for sure until we've seen an image of it.'
是否有东西落到地球，我们只有看到其影像才能确定。
Also, you can't know for sure what the other players are holding and what the next CARDS are going to be.
而且，你也不可能知道对手手里的牌是什么，下一张牌又是什么。
One thing we know for sure is that the British economy will suffer its first recession for 18 years in 2009.
头一件我们可以肯定的事就是英国的经济将在2009年经受18年来的第一次衰退。
The business wants to reduce the cost of the process, but does not know for sure how much it costs per order.
企业希望降低流程的成本，但是无法确定每个订单的具体成本。
One thing I know for sure, to be good in my business I could simply just meet the expectations of my passengers.
我很清楚要干好这一行，需要做的仅仅就是满足乘客的期望。
We can't know for sure how many Kindles Amazon (AMZN) is selling, because the company refuses to release figures.
亚马逊到底卖出了多少台Kindle，我们不得而知，因为公司拒绝公布具体数据。
We don't know for sure, but we do know that every species that is removed … results in some weakening of the ecosystem.
我们完全不知道，但我们知道，每一种物种的灭绝······结果都是在某种程度上对地球生态系统的削弱。
All that Iraqis know for sure is that they have reached another turning-point in their turbulent post-invasion history.
对于所有的伊拉克人民来说都心知肚明，他们纷乱的战后历史又将迎来一个转折点。
But most scientists agree that further studies are needed before we can know for sure whether these farms are feasible.
但是大多数科学家都认为，我们需要进一步的研究才能确认建造这些农场是否切实可行。
There is no way to know for sure how well the last stimulus worked because we don’t know what would have happened without it.
没有确切衡量最后一次刺激计划成效的方法，因为我们不知道如果没有它的话会发生什么。
I will never know for sure whether I was encouraging or discouraging my children's interest in technical work by my example.
我不知道自身的榜样对孩子们在科技方面的兴趣是起了鼓励作用还是反作用。
The only thing we know for sure is that it increases our debt and locks in bigger and bigger interest payments every single year.
我们唯一可以肯定的一点是，它增加了我们的债务而且我们在每一年都会支付更多的利息。
These are the beginnings, yes; but how do you know for sure when you don't know the end, and how do you know, or even surmise, the end?
这是开始，没错；但当你还没有看到结果如何的时候，你怎么能确切地知道，即使是猜测到，结果呢？
This is what I know for sure: in order to be truly happy, you must live along with and you have to stand for something larger than yourself.
我可以非常肯定的是为了追求真正的快乐，你必须为了一些更有意义的事而生活。
Do you remember all those years when scientists argued that smoking would kill us but the doubters insisted that we didn't know for sure?
还记得那些年科学家说吸烟会要我们的命而怀疑者却坚持说我们并不肯定、证据没有说服力、科学没有定论么？
The cause of that disaster has not been determined though, and it is impossible to know for sure whether the system could have prevented it.
尽管那次灾难的起因未有定论，并且也不可能确信系统是否能阻止灾难发生。
The cause of that disaster has not been determined though, and it is impossible to know for sure whether the system could have prevented it.
尽管那次灾难的起因未有定论，并且也不可能确信系统是否能阻止灾难发生。
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