Answer
Choice B.
Work Step by Step
This is a case of uniform circular motion. For the object moving at constant speed in a circle, the acceleration and net force both point inward, toward the center, as proven in section 5-2. The net force has the same magnitude everywhere in the motion: $\frac{mv^{2}}{r}$.
At the top of the circle, the string tension and gravity both point downward, adding together. The tension provides only part of the centripetal force.
However, at the bottom of the circle, gravity points down and opposes the tension, which points up. Thus, the tension minus the weight equals the centripetal force, which means that the tension is maximum there.
