required to

将来可能发生的情况是，他们被要求掌握一些在学校没有学过的知识，以便找到工作。

It may occur in the future that they are ___required ___to possess knowledge of something they didn't study at school in order to get a job.

法律要求您出示有效护照。

You are ___required by law ___to produce a valid passport.

学生参加学校旅行前必须征得父母同意。

Students are ___required ___to ask their parents before going on the school trip.