We don't know why he made so many.

我们不知道他为什么画了这么多。

We don't know why, but about 250 million years ago they all died out.

我们不知道为什么，但大约2.5亿年前它们全部灭绝了。

We don't know why he left.

我们不知道他为什么离开。

We don't know why such things happen.

我们不知道为什么会发生这种事。

We don't know why there is this discrepancy.

我们尚不清楚为什么会存在这种差异。

If we don't know why it died, we can't do anything about it, we can't stop it.

如果不知道鲸鱼死亡的原因我们就没有办法阻止它的死亡。

We don't know why Daniel was last, but we do know that God showed Daniel the clear meaning of the dream.

我们不知道为什么但以理是最后一个， 但我们知道神清楚地给但以理显明了梦的意思。

And even worse -- it's not that helpful, because we might know there was a fever or vomiting, but we don't know why.

更糟的是，它对于我们的研究并没有多少帮助，因为即便我们得知孩子有发烧或呕吐的症状，我们仍然不知道症状背后的根本原因。

We don't know why the brain often interprets these particular odors as off-putting.

我们尚不清楚为何大脑会认为这些特定气味令人讨厌。

That difference between hemispheres is a bit bizarre, and we don't know why it's like that.

南北半球之间的差异实属奇怪，而且我们都不知道为什么会那样。