一、定语从句中关系代词的省略：
在限定性定语从句中,关系代词在从句中充当宾语时,则可省略该关系代词.
Do you remember the school (which/that) we visited last year?
Do you remember the teacher (who/whom/that) we visited last year?
二、名词性从句中的省略：
名词性从句中,只可以省略宾语从句中的第一个that,主语从句、表语从句和同位语从句中的that均不可省略.
He said (that) he liked the book and that it was interesting.（宾语从句）
The reason why he liked the book was that it was interesting.（表语从句）
That the book was interesting was the reason why he liked it.（主语从句）