1, a circle with a radius of 2 cm, a circumference of (12.56) cm and an area of (12.56) cm 2.

2. Enlarge the diameter of the circle by 3 times, the circumference by 3 times and the area by 15 times.

3. The compass draws a circle with a circumference of 28.26 cm, and the distance between its two feet is (4.5) cm.

4. A circle is an (axisymmetric) figure with (countless) symmetrical axes.

5. A semicircle with a radius of 4 decimeters and a circumference of (20.56) decimeters.

Second, judge.

1. The line segment passing through the center of the circle with both ends on the circle is called the diameter of the circle. (right)

The circumference of a semicircle is half that of this circle. (error)

3. When drawing a circle, the center of the circle determines the position of the circle, and the radius determines the size of the circle. (right)

The radius of a circle is 2 decimeters, and its circumference and area are equal. (error)

Third, choose.

The correct relationship between 1, π and 3. 14 is (a).

A.π>3. 14

B.π=3. 14

C.π