VERB
（尤指经过努力后）查明，弄清，确定
If you ascertain the truth about something, you find out what it is, especially by making a deliberate effort to do so.
例句
Through doing this, the teacher will be able to ascertain the extent to which the child understands what he is reading...
这样一来，老师就能确定孩子们对他所读的内容理解多少了。
Once they had ascertained that he was not a spy, they agreed to release him...
一旦确认他并非间谍，他们即同意将他释放。