组成句子的各部分叫做句子成分。句子的成分有：主语、谓语、表语、宾语、宾语补足语、定语和状语。
二. 句子最基本的结构是：主语+谓语
主语：在句子中的位置是放在句首：可以作主语的词类有名词、代词、数词、不定式以及词组、从句等等。
e.g. The boys are playing football now. 名词作主语
Two and two are four. 数词作主语
To learn a foreign language is very useful. 动词不定式作主语 This is a key. 代词作主语。
谓语：谓语放在主语之后，动词作谓语，包括及物动词，不及物动词，系动词。
e.g. The students are reading books.
动词作谓语
表语：放在谓语之后，结构是：主语+谓语(系动词)+表语
用作表语的词有名词，代词，数词，形容词，副词，不定式，词组，从句等等。
e.g.
We are students. 名词作表语
This desk is hers. 代词作表语
Lee is fifteen. 数词作表语
Sarah’s car looks nice. 形容词作表语
Our plan is to plant trees. 动词不定式作表语
Is your father in? 表示地点的副词作表语
宾语：宾语放在谓语之后，结构是：主语+谓语(及物动词)+宾语，宾语分为直接宾语和间接宾语，直接宾语指物，间接宾语指人。
e.g. Please pass me the salt.
间接宾语 直接宾语
用作宾语的词有：名词，代词，数词，不定式短语，名词性的形容词或从句。
e.g.
Do you need any help?
名词作宾语
Would you like to help me? 代词作宾语
He bought ten oranges. 数词作宾语
The teacher wants to take these chairs out of the room.
动词不定式作宾语
宾语补足语：在句子中放在宾语之后，结构是：主语+谓语(及物动词)+宾语+宾语补足语
可以用作宾语补足语的词有：名词，形容词，不定式和分词。名词或者代词+形容词/名词/不定式/分词 e.g.
The good news made me happy. 形容词作宾补
Did you hear her sing just now? 动词不定式作宾补
I saw him cleaning the window yesterday. 分词作宾补
Let us have a rest. 不定式短语作宾补
状语：一般放在句尾，有时放句首或句中。作状语的词有：副词，介词短语、词组，不定式短语，分词短语第以及从句。
e.g. Immediately he started to sing. 副词放句首，作状语
I’m never late. 副词放句中作状语
He drives fast. 副词放句尾作状语。
Please park the car in front of the building. 介词短词作状语放句尾
They went to Shanghai to have a meeting. 动词不定式作状语
Jack watched TV day and night. 词组作状语
定语：请记住有名词或代词的地方都可以有定语。
一般情况下单个的名词，代词，形容词放在所修饰的名词之前，而词组、短语、从句要放在所修饰的名词之后。
可以用作定语的词有：形容词，代词，数词，名词或名词所有格、介词短语，不定式短语，词组，分词短语和从句。
e.g.
Ben is an old man. 形容词用作定语，放在名词之前。
Do you want another cake?
代词用作定语放在所修饰的名词前
The girl asked her mother two questions.
数词用作定语放在所修饰的名词之前。
The worker put the flowers in a paper bag.
名词用作定语放在所修饰的名词之前。
Who’s the man over there?
介词短语作定语放在所修饰的名词之后。
Could you bing me something to drink, please? 动词不定式作定语，放在不定代词之后。
The plane that can fly is a machine.
从句用作定语放在所修饰的名词之后。
三. 句子的结构：简单句，并列句和复合句 首先看简单句的五种基本句型
(1)主语+谓语(不及物动词) e.g. Summer is coming.
(2)主语+谓语(连系动词)+表语。 e.g. You are very busy.
(3)主语+谓语(及物动词)+宾语 e.g. Mr Liu teaches English.
(4)主语+谓语(及物动词)+宾语+宾语 e.g. Mum gave me a dictionary. = Mum gave a dictionary to me.
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