I often think of the moment when I saw the UFO.
2．我们通常用关系副词where引导先行词是place，house，city，country，city，world等的定语从句。
如：The police searched the house where the thief had stayed.
This is not a family where bad behavior goes unpunished.
3．我们通常用关系副词why引导先行词是reason的定语从句。
如：I don’t know the reason why the house is so dirty.
4．在更加正式的英语中，where，when和why能够被介词＋which 所替代。
如：The study is the place where/in which I often have talks with my father.
This is the reason why/for which my parents got home earlier.
It rained the whole day when/on which he traveled with his family.
一 定语从句：非限制性定语从句
1．非限制性定语从句是一个为主句添加额外信息的从句，在非限制性定语从句前通常有个逗号。
如：Amy, who took weight-loss pills, now realizes that health is important.
My pills are in the bathroom, where I always keep them.
2．当先行词是整个主句时，可以用which来引导定语从句。
如：He missed the show, which was a great pity.
3．我们可以用all＋whom/which 来表示全部数量，用some of＋whom/which来表示部分数量。
如：I am doing different types of exercises, all of which are quite helpful to my health.
Many people, some of whom are not overweight, are going on diet.
1．附加疑问句是放在陈述句后面的短问句。它们通常被用在口语中来引出一段对话，以一个更加礼貌的方式来询问信息，温柔的发号施令或要求某人做某事。我们用附加疑问句来询问意见或征求同意。 当我们用附加疑问句来询问意见时，为了期待对方能同意我们的观点，附加疑问句会用降调来表达。
当我们用附加疑问句来征求同意时，我们实际上是在询问我们自己也不太能确信的事情，这时候附加疑问句会用升调来表达。
2．附加疑问句的构成有以下几种：
1）在肯定的陈述句之后，我们会用否定的附加疑问句。在否定的陈述句之后，我们会用肯定的附加疑问句。
