This is how we know it is the last hour.

从此我们就知道如今是末时了。

youdao

Also, it is cylindrically symmetric around the bonding axis, so this is how we know that it's a sigma orbital.

此外，它关于键轴是圆柱对称的，这就是为什么我们知道它是sigma轨道。

youdao

We don't know the answer, because studies done on how reliable this machine is have not yet been duplicated.

我们不知道答案，因为关于这台机器可靠性的研究还没有被重复。

youdao

"that are against this move-are asking is this, 'How do we know that the Americans and the West are basically going to let the Russians live up to their promise of giving the uranium back?

VOA: standard.2009.10.28

Also, it is cylindrically symmetric around the bonding axis, so this is how we know that it's a sigma orbital.

此外，它关于键轴是圆柱对称的，这就是为什么我们知道它是sigma轨道。

麻省理工公开课 - 化学原理课程节选

OK, so now the question is, how do we know the first place that this is a suitable reductant?

好的，现在的问题是，我们如何能知道第一步中,镁是一个合适的还原剂？

麻省理工公开课 - 固态化学导论课程节选

In relation to how does this end, we cannot with certainty know how this is going to end, and those of us who did support the government not with enthusiasm but with resolve last week have to have the humility to acknowledge that.

BBC: Transcript of Douglas Alexander interview

How do we know this is our first sun?

NPR: What Makes Our Solar System Special?

How do we know this is Obama's plan?

CENTERFORSECURITYPOLICY: Obama's abandonment of America