This important lesson by Professor Wang teaches primary students how to ________ themselvesfrom danger.[ ]

______ nice time the boys had playingfootball with the national team last Sunday!

Riding bikes has advantages __________driving cars ________ many aspects.

My documents are always ______ out according to the contents(内容) and dates so that I have no trouble in finding them when they _______

It was impolite of him ____without ____good－bye