Through doing this, the teacher will be able to ascertain the extent to which the child understands what he is reading. [VERB noun]

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. [VERB that]

一旦确认他并非间谍，他们即同意将他释放。

Take time to ascertain what services your bank is providing, and at what cost. [VERB wh]

花些时间确认一下你的银行会提供什么样的服务，费用是多少。