Answer: 2, 3

The second question:

Answer: 6

The third question:

Answer: 8, 30

The fourth question:

Answer: 6800,830

The fifth question:

Answer: 9, 8

The sixth question:

Answer: square meters, centimeters

Question 7:

A: A.

Question 8:

A: A.

Extended information This paper examines the area unit:

When the space occupied by an object is a two-dimensional space, the size of the space occupied is called the area of the object, which can be plane or curved. Square meters, square decimeters and square centimeters are recognized units of area and can be expressed as (m? ，dm？ ，cm？ )。

Area is a quantity indicating the degree of a two-dimensional figure or shape or plane layer in a plane. A surface region is a simulation on a two-dimensional surface of a three-dimensional object. Area can be understood as the amount of material with a given thickness, which is necessary to form a shape model.