2.定语从句与同位语从句的区别
同位语从句大多由连接词that引导，常跟在下列名词后面，如fact，idea，opinion，news，hope，belief等。同位语从句用来解释说明这些名词的具体含义和内容。定语从句对所修饰的名词加以修饰限定，即说明其为此人(事物)而非彼人(事物)。如：
We are familiar with the idea that all matter consists of atoms.(同位语从句)
The news that we are invited to the party is very encouraging.(同位语从句)
This is the best article that has been written on the subject. (定语从句)
4.定语从句与what引导的名词性从句的区别
what只能引导名词性从句，在从句中充当主语、宾语或表语，但总是包含着定语从句的含义，很容易与定语从句混淆。定语从句的引导词前面都会有先行词，而what前面则没有任何先行词，此时what=先行词+that。试比较：医学.全在线www.med126.com
He always means what he says.
That's the only thing that he says.
That's what I want to say.
That's all (that) I want to say.
This is what I can give you.
This is all the money that I can give you.
(二)比较状语从句
1.比较状语从句的种类
(1)同级比较。
英语中表示同级比较的词有as+形容词或副词原形+as；the same as，not so+形容词或副词原形+as(不如…)等。
例1：Do you enjoy listening to records? I find records are often _____, or better than an actual performance. (1996.1)
［A］ as good as［B］ as good［C］ good［D］ good as
答案为［A］。这里的as good as和better than 由or连接，构成并列关系。
例2：The elimination of inflation would ensure that the amount of money used in repaying a loan would have _____ as the amount of money borrowed.
［A］ as the same value［B］ the same value［C］ value as the same［D］ the value is the same
答案为［B］。the same...as为固定用法。
(2)差级比较。
英语中的差级比较，仅限于两者之间，常由形容词或副词的比较级形式+than 构成。此外还需要注意以下几点：
①相比较的内容在语法形式或结构上要保持一致。
英语中，为了避免重复通常用that，one，those来代替前文出现的同类事物，其中that可以代替可数名词和不可数名词，而one只能代替单数可数名词，those只能代替复数可数名词。如：
No bread eaten by man is so sweet as _____ earned by his own labour. (1994.8)
［A］ one［B］ that［C］ such［D］ what
答案为［B］。that代替的是不可数名词bread。
②表示倍数的比较形式常为：修饰语 + as...as.../more...than...。有时第二个as，than后面的比较内容会省略。例如：
Smoking is so harmful to personal health that it kills _____ people each year than automobile accidents. (1999.2)
［A］ seven more times［B］ seven times more［C］ over seven times［D］ seven times
答案为［B］。倍数+ more ...than...为固定结构。
