potential and kinetic energy select the point where the roller coaster cars have the greatest kinetic energy.

Explanation:

Step1: Recall energy - conversion principle

Kinetic energy $K = \frac{1}{2}mv^{2}$ and potential energy $U = mgh$. Total mechanical energy $E=K + U$ is conserved (neglecting friction). Lower height means lower potential energy and higher kinetic energy.

Step2: Analyze the points

Point B is the lowest point on the roller - coaster track. At this point, the roller - coaster cars have the least potential energy (since $h$ is minimum), so they have the greatest kinetic energy.

Answer:

B