Since the example circle is not shown, I can not answer thoroughly, but I will try my best.
The equation of a circle: (x - h)² + (y - k)² = r², where (h,k) is the center and r is the radius of the circle.
This means that for the radius to be two units, the right side of the equation is 2² = 4. So either B or d can be right.
Depending on the center of the given circle, we could narrow down to our final answer. If the center is (4,5), B is right, and if (5,4) is the center, D is right.
