Answer:
The part of the sphere labeled A is the radius.
Explanation:
A sphere is a 3 dimensional object with a definite volume formed from a circle. Some parts of a sphere are: center, radius, circumference, diameter etc. The radius is a major part of a sphere. The radius of a sphere is a measure of the length of the distance from its center to its circumference. The distance, i.e radius, is constant considering various points on the circumference of a sphere.
Since C represents the center of the sphere, the part of the sphere labeled A is the radius.