ascertain
verb [ T ] formal uk/ˌæs.əˈteɪn/ us/ˌæs.ɚˈteɪn/
弄清，确定，查明
to discover something
The police have so far been unable to ascertain the cause of the explosion. 警方到目前为止尚未查明爆炸原因。
[ + question word ] Have you ascertained whether she's coming or not? 你问清楚了吗，她来还是不来？
确信
to make certain of something
[ + that ] I ascertained that no one could overhear us before I told Otto the news. 确信没有人能听到我们的谈话之后，我才把这个消息告诉了奥托。