ascertain 造句？急！先谢谢了

Moody man is really difficult to ascertain. (喜怒无常的人真难捉摸)

I can ascertain that you are a thief.

我可以确定，你是个小偷。

查明：The policeman is ascertianing the truth about the thing.
警察正在查明这个事情的真相。

The police are trying to ascertain what really happened.
警方正设法查个水落石出。