Adverbial clauses of time (时间状语从句) 引导时间状语从句的从属连词有：when，while，as，whenever，before，after，since，till，until，as soon as，once，the moment，immediately，no sooner...than，hardly...when，by the time，every time，the last time...等引导。

Period Four　Grammar(1) & Grammar(2)