二、引导非限定性定语从句时,只能用which(不用that)。例如:

　　Heat is another form of energy, which is as important as other kinds of energy.热是另一种形式的能量,与其他形式的能量一样重要。

　　从句表补充说明,而且关系代词which不能换成that。

　　三、引导非限定性定语从句的which可以指代前面的先行词,也可以指前面整个句子的含义。例如:

　　That Peter will marry Alice, which has not been announced yet, has spread around.彼特要娶爱丽斯这件事还没宣布,却已传得沸沸扬扬。

　　句子中的which指"彼特要娶爱丽斯"这整个句子的意思。

　　四、除which外,还可用when, where, who等关系代、副词引导非限定性定语从句。例如:

　　After graduation, I decided to stay in Chongqing, where I spent my childhood and four years of college life.毕业后,我决定留在重庆,在那里我曾度过了我的童年和四年大学生活。

　　Albert Einstein left Germany for the United States during World War II, when Jews were badly treated in Germany.第二次世界大战期间,爱因斯坦离开德国去了美国,那时犹太人在德国受到不好的对待。

　　五、在限定性定语从句中作宾语时,引导词可以省略,但引导非限定性定语从句的关联词不能省。试比较:

　　He was eager to go to the hospital to see his stepmother, whom he loved and respected as his own mother.他急于想去医院看望他的继母,他把他的继母当作亲生母亲一样热爱和尊敬。

　　The American journalist (whom / who) the announcer mentioned in the news broadcast is said to have been killed by the gangsters.播音员在新闻广播中提到的那位美国记者据说已经被匪徒杀害了。

　　两例中的关系代词都在从句中作宾语.由于第二例是限定性定语从句,可以