（一）、在定语从句中，当先行词指物时，下列情况的关系词宜用that而不用which
1）先行词被①形容词最高级 ②序数词修饰。
2）先行词为all、much、little、none、few、one、anything，everything, nothing 等不定代词或被every、any、some、no、few、the only、the very等词修饰时。
3）先行词中既有人又有物时。
he was looking pleasantly at te children and parcels that filled his bus.
4）先行词在主句中作表语关系词在从句中作表语时。
the village is no longer the one that was 5 years ago.
5）当主句中含有疑问词which、who、that时。
which are the books that you bought for me ?
6）在there be句型中时，只用that。
二）、指物时，宜用which而不用that的情况
1）在非限制性定语从句中
football, which is very interesting game, is played all over the world.
2）在关系词前有介词时
is that the house in which you once lived?
3）当先行词本身是that时
三)、关系词who与that指人时，也有不同情况分别用不同的关系词
1）先行词是为anyone、those、someone、everyone、one等词时，关系词用who。
2）当主句是who作疑问词时，关系词用that。
who is that girl that is standing by the window?
四）、关系代词as,在从句中作主语、宾语和表语。
1）先行词被such/as/so/和the same修饰，或句型as many（much）中，作定语时，从句都用as 引导。
such books as you bought are useful.
the school is just the same as it was 10 years age.
注意：区别①such/as/so … that … 及the same … that …引导的结果状语从句。they are such lovely children that we love them much.
②such/as/so … as …及the same … as … 引导定语从句。i want to use the same tool as you used just now.
2）先行词为一句话时，定语从句用as和which引导。
区别：①意义上：as 含有“这点正如……一样”。
②位置上：as 从句可置句首，也可在另处（which不能放在句首）。
he didn’t pass the exam, as we had expected.
there is lots of air in loose snow, which can keep the cold out.
as is known, the earth is round, not flat.
五）、指人时，whom的用法情况
（1）在非限制性定语从句中
（2）在关系词前有介词时
六）、关系副词when与where、why、
when 指时间 = in / at / on / during which
where指地点 = in / at / from / which
why指原因 = for which
当先行词为way、day、reason、time时，可用that作关系副词。（非正式场合）
i don’t like the way that he talks.
当time作先行词时，关系词可以省掉。
this is the first time i h**e given you a lesson in french.
七）、 whose是关系代词，修饰名词作定语，相当于所修饰成分的前置所有格。它引导的从句可以修饰人和物， 当它引导的从句修饰物体时， 可以与 of which 调换，表达的意思一样。
注意。1.当介词放在关系代词前面时，关系代词只能用which/whom即“介词+which/whom"且不能省略。
the school in which he once studied is very famous.
2.“介词+关系代词”前可有some, any, none, both, all, neither, most, each, few等代词、数词或者名词。
in the basket there are quite many apples, some of which h**e gone bad
判断介词和关系代词。
方法一： 用关系代词，还是关系副词完全取决于从句中的谓语动词。不及物动词后面无宾语，就必须要求用关系副词或者是介词加关系代词；而及物动词后接宾语，则要求用关系代词。例如：
this is the mountain village where i stayed last year.
she still remembers the day on which (when) she own the prize.
方法二： 准确判断先行词在定语从句中的成分(主、谓、宾、定、状)，也能正确选择出关系代词/关系副词。
i never forget the days which we spent together. (which做宾语)
i never forget the days when we spent our holidays together.(when 做状语)
非限制性定从。
1. which引导的非限定性定语从句作用是说明前面整个句子的情况或主句的某一部分
2.当先行词是专有名词、物主代词或指示代词所修饰时，其后的定语从句通常是非限制性的。
my house, which i bought last year, has got a lovely garden.
3.非限定性定语从句可将整个主句作为先行词， 对其进行修饰， 这时从句谓语动词要用第三人称单数，例如：
he seems not to h**e grasped what i meant, which greatly upsets me
4. 有时as也可用作关系代词
as is well-known to us, smoking is harmful to our health.
注意。that和why 不能用于非限制性定从中。
只有which和whom前面能跟介词。
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