我不知道是什么起的作用，但是我确实觉得好多了。

I don't know what it was that did the trick, but I am definitely feeling much better.

《牛津词典》

直到今天，我仍然不知道是什么跟着我回家，但我很害怕，我宁愿不知道。

To this day, I still have no idea what followed me home but I was terrified and I'd rather not find out.

youdao

我不知道是什么，我不知道什么时候，但我知道它将会发生。

I don't know what and I don't know when, but I know it's going to happen.

youdao