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。
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。
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。
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。
Just as on smoking, voices now come from many quarters insisting that the science about global warming is incomplete, that it's OK to keep pouring fumes into the air until we know for sure.
就像吸烟一样，现在来自许多方面的声音坚持认为，有关全球变暖的科学是不完整的，在我们确定之前，继续向空气中排放烟雾是可以的。
Well, I don’t know for sure either.
我也不知道。
However, we don't know for sure.
然而，我们仍然不能确信。
但我也不敢肯定。
我们可能永远无法确定。
您肯定的事情是什么？
你怎么能把握得住呢？
你不可能确切知道。
我不能肯定。
That is the only thing we know for sure.
这是我们唯一确定的事情。
Don't know for sure, but yes, I think there is some.
还不能确定，但答案是肯定的，我认为有些产品会是这样的。
One thing we know for sure — it is not the Higgs boson.
只有一件事我们相当确定——一定没有希格斯玻色子。
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。
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。
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。
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。
Here's what we know for sure, based on comments from Microsoft execs.
下面是我们根据微软execs的回复所得到的信息。
Or it's a case of "won't dignify with a response" – we can't know for sure.
或者，这只是一种“不高贵的回应”情况，我们也无法确定事情的真假。
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？
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？
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