引导时间状语从句的连词较多,主从句时态搭配以及谓语动词的动作时间长短性等用法特点也各异。特别是九年级教材中出现的when和while的用法特点,是同学们需要掌握的重点,也是难点。时间连词when的用法特点一般来讲,when的意思相当于at that time(在……时刻),因此从句的谓语动词通常是非 There are many conjunctions in the guide time adverbial clauses, the collocation of the main clauses and the length of time of the predicate verbs. Especially the nineteenth grade when and while the usage of the characteristics of the textbooks, students need to grasp the key points, but also difficult. Usage of time conjunders when Generally, the meaning of when is equivalent to at that time, so the predicate verb of a clause is usually non-