在英语中that和which可以省略的从句是
定语从句，省略的条件是现行词在从句中作宾语才可以省略，其他情况则不可以省略。
例如1：I can't find the book (which/that) I bought last month. 现行词the book在从句中作bought的宾语，可以省略。
例2：The book which / that was bought last month was lost yeaterday. 这题现行词the book在从句中作主语，此处不能省略。
还有一种that可以省略的的从句，就是
宾语从句。
例如：Our teacher suggests (that) we should read English every day. 这里suggests后面的是宾语从句，that可以省略。
注意：如果一个动词后面接两个或者两个以上的宾语从句时，第一个从句的that可以省略，但从第二个从句开始that不能省略。
例如：The teacher said (that) we should read English every day and that there would be an English exam next week.这里said连接两个宾语从句，第一个从句的that可省可不省略，第二个不可以省略。