【答】同位语从句和定语从句的区别是：同位语从句是对先行词起解释或补充说明的作用，可以去掉而先行词的意思依然完整；而定语从句（限制性定语从句）对先行词起限定或修饰的作用，去掉后先行词的意思就不完整。

2、判断依据：that在同位语从句中不充当成份，没有实际意义，一般不省略（少数情况除外），that在定语从句中要充当句子成份，起代替先行词的作用及连接先行词与定语从句的作用，作主语时不能省略，而作宾语时可以省略。

如：1) We were very happy at the news that our team had won the match. (同位语从句）2) We were very happy at the news (that) you told me just now. (定语从句）。