一、宾语从句的连接词
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,在口语中常被省略。
eg. He knew (that) he should work hard.
2.连词if 、whether,它们起连接作用,在从句中不作句子成分,作“是否”解,在口语中多用if。
eg. Tom don't know if/whether his grandpa liked the present.
He asked me whether or not I was coming.
一般情况下,if 和whether可以互换,但以下3种情况只能用whether: