1定语从句关系词一、先行词指物，只用 that 不用 which 的特殊情况：1、先行词是不定代词 all, little, few, something 等或被不定代词 any, each, every, much, (a) little, (a) few 等修饰时 Eg. Do you have anything that I can do for you? / There is much (work) that he can do here. 2、先行词是形容词最高级或被最高级所修饰时Eg. This is the most interesting story that I have heard.3、先行词是序数词（以及 last）或被序数词所修饰时Eg. This is the first city that I visited in China.4、先行词前有 the very, the only, the just 等修饰时Eg. This is the very pen that I lost yesterday.5、一个句子带有两个定语从句，一个已用 which, 为避免重复，另一个只能用 that。
Eg. They built up a factory which produced things that sold well.6、先行词既有人又有物时Eg. Do you remember the things and persons that we often talked about in our childhood?7、主句是以 who 或 which 开头的特殊疑问句时Eg. Who is the girl that is standing there? / Which is the car that you bought last night?注：当先行词指人时，除了第 6、7 条以及有 the same 修饰不能用 who 之外，其他情况既能用 that 又能用 who/ whom 引导二、先行词指人，只用 who/whom 不用 that 的情况：1、先行词是不定代词 one, ones, anyone, anybody 等时 Eg. Is there anybody else who would speak at the meeting?2、先行词是 those 时。
Eg. Those who want to visit the museum sign up here.3、非限定性定语从句中，无论先行词指人还是指物，都不用 thatEg. I have two sons, one of whom is abroad.4、一个句子带有两个定语从句，一个已用 that, 为避免重复，另一个只能用who/whom Eg. The girl that is singing is my classmate who studies very hard.5、在 there be 开头的句子里 Eg. There are many old men who don’t like pop music.6、关联词紧贴介词，不能用 that( 指人用 whom 指物用 which)Eg. Do you know the boy with whom the teacher is talking?7、先行词有较长的后置定语，且定语为物，为明确关系，只能用 who/whomEg. I met a foreign from the United States who could speak Chinese very well.三、关系代词 as 与 which 的用法比较：1、as 和 which 均可以代整个主句，引导一个非限定性定语从句，有时可以换用。
但是它们有区别：1）as 从句可以在主句前、后甚至中间，而 which 从句只能放在主句后 Eg. He was against the idea, as/ which was expected.As was expected, he was against the idea.2）as 有“正如、正像、像……那样”之意，并已形成固定搭配，而 which 既没有上述含义，也没有类似的固定搭配Eg. As is known to all, the earth goes round the sun. 类似的结构还有：as was usual 像往常那样，as is reported 像报道的那样，as anyone can see 正如大家所看到的，as is often said 正如常说的那样……2、as 引导的限定性定语从句，常用于 the same…as, such…as, such as 等固定搭配中2Eg. It is the same book as I bought last week. 这本书和我上周买的那本相同Such people as/ People such as you describe are rare nowadays. 你描述的那种人现在已经很少了。
注：the same…as 引导的从句，指与先行词相似的同类事物；而 the same…that 从句指与先行词同一事物Eg. This is the same bag as I lost. 这个包与我丢的那个包一样This is the same bag that I lost. 这正是我丢的那个包。