Do型：
Leave me alone!
Get out!
Sit down,please.
Wake up.
Stand up.
Open the door now.
Do it now.
Be型：
Be quiet!
Be nice.
Be a good boy.
Don't be so mean.
Don't be late.
Let型：
Let's go.
Let's dance.
Let me help you.
Let's begin the lesson.
例子太多了,记住祈使句都是动词原形开头.否定式是don't +动词原形