People often ask me if I know the secret of success, and if Icould tell others how to make their dreams come true. Myanswer is, you do it by working.--Walt Disney
人们时常问我是否晓得成功的诀窍,能否告诉别人怎样使他们的梦想成为现实。我的回答是:身体力行。--华特·迪士尼(美国实业家)

1. The time when I first met Nelson Mandela was a very difficult period of my life.
2. The school where I studied for only two years was three kilometres away.
3. I don't know the reason why he came so late.
4. I will never forget the time that/which we spent in the park.
5. This is the factory that/which makes radio parts.
6. That's the reason that/which he explained to us.

(1)句1中，关系副词when在定语从句中作时间状语;
(2)句2中，关系副词where在定语从句中作地点状语;
(3)句3中，关系副词why在定语从句中作原因状语;
(4)句4,5,6中,先行词虽是表示时间、地点、原因的词,但在从句中充当主语或宾语,而不是状语,故应用that/which 。