复合句是由主句＋从句构成,它是英语中比较复杂的句子结构.一般来说,英语中一个句子只能有一个谓语,如果出现两个谓语动词,那么其中一个谓语动词只能以从句的形式或并列句或非谓语动词的形式出现.所谓从句是指从属于主句的句子,由从属连词连接.从句的种类有很多,但根据其性质和作用可以分为：名词性从句,形容词性从句（即定语从句）,副词性从句（即状语从句）三大类.
一、名词性从句：即从句在整个句中起名词作用,分别可以作主语、宾语、表语、同位语等,所以这类从句包括主语从句、宾语从句、表语从句和同位语从句.
考点一：主语从句：主要考查主语从句的引导词；主句的谓语动词,一般用单数.如：
1.That the earth goes around the sun is well-known to everybody.
( = It is well-known to everybody that the earth goes around the sun.)
2.Whether he will come to the meeting is up to his boss.（此时不能用if ）
3.Who will come to the dinner remains a question.
4.What you have said is convincing.
5.How the ancient Egyptians built the pyramids puzzled people for centuries.
6.Why the murderer came back to the scene of crime is a psychological problem.
同时,需要注意主语从句的一些常见句型.如：
考点二：宾语从句：主要考查宾语从句的引导词和引导词的省略以及从句的语序.如：
1 He believed that walking under a ladder brings bad luck.
2.We can learn what we do not know from TV programs.
3.Tell me which of the books is the right one.
考点三：表语从句：be动词或者系动词后面跟主语补足语.
1.The assumption is that things will improve.
2.China is not what it used to be.
3.The doctor’s dilemma is whether he should tell a lie to the patient.