Definition
Used to express that something is impossible to know or determine; only God would know.
天知道
God only knows why he would do that.
只有老天知道他為什麼會那樣做。
I really don't know the answer to this question; God only knows what it is.
我真的不知道這個問題的答案，只有上天知道。
God only knows what she'll do next.
只有老天知道她接下來會做什麼。