句子成分之谓语

谓语
谓语（predicate verb）是对主语动作或状态的陈述或说明，指出“做什么”、“是什么”或“怎么样”。谓语动词的位置一般在主语之后。
谓语由动词充当，说明主语所作的动作或具有的特征和状态。依据其在句中繁简程度可把谓语分为简单谓语和复合谓语两类。不论何种时态、语态、语气，凡由一个动词（或动词词组）构成的谓语都是简单谓语。

简单谓语：
由动词、动词短语或者动词的时态构成。如：
I like walking. (一般现在时主动语态)

I made your birthday cake last night. (一般过去时主动语态)

It is used by travellers and business people all over the world. (一般现在时被动语态)

复合谓语：
1.由情态动词或助动词+不带to的动词不定式构成。如：
You may keep the book for two weeks.
He has caught a bad cold.
My sister is crying over there.
I have been waiting for you all the time.
I would stay at home all day.

2.由系动词加表语构成。系动词不能单独作谓语，要和表语一起作谓语。
We are students.
Your idea sounds great.