大概分为四l种。
1.连词that:只起连接作用,在从句中不作句子成分,也无词汇意义,在口语中或非正式文体中常被省略。例如: 1)He knew(that)he should work hard.
2)I am glad(that)you've passed the exam.
2.连词whether或if:它们起连接作用,在从句中不作句子成分,作“是否”解,口语中多用if。例如: 3)Do you know whether he will ride here at 8 tomorrow morning?
4)Tom didn't know if/whether his grandpa liked the present.
作“是否”解的if和whether在具体用法上差别较大,同学们不易掌握。在宾语从句中用whether没有用if时受到那么多限制。例如:
5)He asked me whether or not I was coming.他问我是否要来。(该句中的whether不能换成if,因为if不能与or连用。)
3.连接代词who,whom ,whose,what, which:它们起连接作用,作句子成分,各有其自己的意义。例如:
6)The teacher asked the new student which class he was in?(武汉市)(which引导宾语从句,在从句中作定语,修饰class,意为“哪个”。)
7)Can you tell me whom he is waiting for?(天津市)
4.连接副词when,where, why,how:起连接作用,分别作时间、地点、原因、方式状语,各有其自己的意义。例如:
8)I wonder where he got so much money.对他从哪里弄到那么多钱我感到疑惑。