句子成分主语（subject）: 句子说明的人或事物
The sun rises in the east
（名词） He likes dancing
（代词）Twenty years is a short time in history
(数词)Seeing is believing
（动名词） To see is to believe
（不定式） What he needs is a book
（主语从句）It is very clear that the elephant is round and tall like a tree
（It 形式主语，主语从句是真正主语）谓语（predicate）: 说明主语的动作、状态和特征
We study English
He is asleep
表语（predicative）: 系动词之后的成分，表示主语的性质、状态和特征
He is a teacher
（名词） Seventy-four
You don’t look it
（代词）Five and five is ten
（数词）He is asleep
（形容词） His father is in
（副词） The picture is on the wall
( 介词短语)My watch is gone / missing / lost
（形容词化的分词）To wear a flower is to say “I’m poor, I can’t buy a ring
（不定式）The question is whether they will come
（表语从句）（常见的系动词有: be, sound（听起来）, look（看起来）, feel(摸起来，smell（闻起来）, taste（尝、吃起来）, remain（保持，仍是）
