at which point(s) does the pendulum have the greatest potential energy?\na only\nb only\nc only\nboth a and c

Explanation:

Step1: Recall potential - energy formula

The gravitational potential energy of a pendulum is given by $U = mgh$, where $m$ is the mass, $g$ is the acceleration due to gravity, and $h$ is the height above the lowest - point.

Step2: Analyze height at different points

At points A and C, the pendulum is at its maximum height above the lowest - point B. At point B, the height $h = 0$ (relative to itself), so the potential energy is minimum. At A and C, the height is maximum, so the potential energy is maximum.

Answer:

D. both A and C