________________________(下课的时候), we began our writing. John sings________________（边走）. _________________________（我们看电视的时候）, he was writing a composition.

When the lesson was over

as he walks

While we were watching TV

注意：

1. when, as, while 的区别

when: 持续性／非持续性动词都可 as: 当；一边…一边；随着 while:持续性动词／　进行