Hi!
The given line is a radius.
What's the difference between a diameter and a radius?
A radius begins from the center of a circle (or sphere) and goes to the end, and it's a straight line.
A diameter is the longest distance between 2 random points on a circle, so it goes all the way across.
In this problem, the line starts at the middle of the circle and goes to the end, so it is, in fact, a radius.
It's not a diameter because it can not go all the way across, since we don't even have all of the sphere.
