句子结构和成分
句子分类
句子按结构可分为简单句、并列句和复合句。
考点1.简单句
只有一个主语(或并列主语)和一个谓语(或并列谓语)。如：
He often reads English in the morning.
Tom and Mike are American boys.
She likes drawing and often draws pictures for the wall newspapers.
（画线部分为并列谓语，只有一个主语，仍为简单句。）
改错：
It not only costs little money but also comfortable.
考点2.并列句
改错：
①.He likes English, his English is very good. ×
②.His wife was ill, he had to stay at home. ×
当一个句子中含有两个简单句时，就要考虑两个简单句的连接问题了。直接用逗号连接两个简单句是错误的。
这时我们可以用and, but, or等并列连词来连接这两个句子；也可以用分号（;）来连接。此时，这两个简单句（此时也可称作分句）之间是并列关系，不能说一个分句作了另一个分句的什么成分。
用并列连词或分号连接起来的句子是并列句。
上两句可以改为：
①.He likes English；his English is very good. (用分号连接)
He likes English, so/and his English is very good.
②.His wife was ill; he had to stay at home. (用分号连接)
His wife was ill, so/and he had to stay at home.
考点3.复合句
A.用从属连词连接的句子是复合句。
还先看上面的两个错句：
①.He likes English, his English is very good.×
②.His wife was ill, he had to stay at home. ×
我们还可以用从属连词来连接。这两句话可改为：
①.Because he likes English, his English is very good.
When he likes English, his English is very good.
②.Because his wife was ill, he had to stay at home.
When his wife was ill, he had to stay at home.
先看第一个句子。当用because连接时，译为“因为他喜欢英语，（所以）他的英语非常好”。主要说的是“他的英语非常好”，“他喜欢英语”是他英语好的原因。因此：“his English is very good”是主句，“because he likes English”是原因状语从句。当用when连接时，译为“当他喜欢英语时，他的英语非常好”。主要说的是“他的英语非常好”，“他喜欢英语”是他英语好的时间。因此，“his English is very good”是主句，“when he likes English”是时间状语从句。
同理，句②修改后，前面分别为原因状语从句和时间状语从句，后面是主句。
像上面这样，用从属连词连接两个简单句之后，一个句子是主要的（主句），另外一个句子（从句）是说明主要句子发生的时间、原因、条件等，这样构成的句子称为复合句。
B.当简单句的一个成分从词或词组变为句子时，整个句子就成为复合句了。从
词或词组升级后的句子是从句，除从句以外的是主句，整个句子是复合句。
①The boy over there is my brother. （只有一个主谓结构，是简单句。）
The boy who is wearing a hat is my brother.
（当over there变为who is wearing a hat时，句子就含有两个主谓结构，一个是The boy is my brother，是主句；who is wearing a hat是the boy的定语，称为定语从句。who既作从句成分，又起着从属连词的作用。）
②I was doing my homework at six. （只有一个主谓结构，是简单句。）
I was doing my homework when he came in.
（I was doing my homework是一个主谓结构，he came in也是一个主谓结构。
后面一个主谓结构作前一个的时间状语，是时间状语从句。因此本句是复合句，when是从属连词。）
③I t is wrong. （只有一个主谓结构，是简单句。）
What he said is wrong.
（what he said，是一个主谓结构。What he said is wrong. 是另外一个主谓结构，What he said作主语，is wrong系表结构作谓语，因此，本句是复合句。What he said是主语从句；what既作从句成分又起着从属连词的作用）
从上面这几个句子，我们可以看出：
C.一个句子如果含有从句，如名词性从句（主语从句、宾语从句、表语从句和
同位语从句）、定语从句和状语从句等，这个句子就是复合句。
练习1.判断下列句子是简单句、并列句还是复合句。
1.We often study Chinese history on Friday afternoon.
2.The boy who offered me his seat is called Tom.
