1．当先行词是all, much, anything, nothing, little, none等不定代词时(something, everything, anything作先行词时，关系代词偶尔也可以用which)
She told me everything that she knew.
她把她所知道的一切都告诉了我。
2．先行词既有人又有物时
I can remember well the persons and some pictures that I saw in the room.
我能清楚地记得我在那个房间所见到的人和一些照片。
3．先行词为序数词或被序数词修饰时
The first place that they visited in Guilin was Elephant Trunk Hill.
在桂林他们参观的第一个地方是象鼻山。
4．先行词为形容词最高级或被形容词最高级修饰时
This is the best film that I have ever seen.
这是我看过的最好的电影。
