I don't know why, but it's close to my heart.

我并不知道为什么，但是它是如此贴近我的心。

youdao

I don't know why I did that. Perhaps it was nervousness, perhaps it was because, when you get very close, one to another, it is very hard not to smile.

我不知道自己为何有这般反应，也许是过于紧张，或者是当你如此靠近另一个人，你很难不对他微笑。

youdao

I don't know why a quarrel broke out between the two neighbours because they used to be close friends.

我不知道为什么这两个邻居之间会发生争吵，因为他们以前曾是很亲密的朋友。

youdao