v.  弄清，确定，查明 ≈ establish

• ascertain sth from sb/sth  弄清楚某事

• ascertain whether/what/how/that…

• It can be difficult to ascertain the facts.

  可能难以查明事实真相。

• Police had ascertained that the dead man knew his killer. 警方确定死者认识凶手。

• You should ascertain the level of insurance cover from the car rental company.

  你应该向汽车租赁公司打听清楚保险的范围。

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

  通过这样做，老师将能确定这个孩子对他正在读的内容的理解程度。