Question

. "Sit down and be quiet!" What type of sentence is this?​

Answer 1

it is an imperative sentences

Answer 2

This is an imperative sentence.

Imperative sentence is a sentence expressing an order or request or advice.

Examples:

1.       Run fast.

2.       Take the lead.

3.       Don’t waste your entire strength at the start.

Explanation

Imperative sentence starts with the First form of the verb. Negative imperative sentence starts with 'Don't'.  

Example: Don't go there. Don't make a noise here.