The correct answer to this question is C, at the top of the hill before the red arrow. Potential energy is defined as the stored energy of a position, which is possessed by an object. Gravitational and Elastic energy are the two types of potential energy.
This question corresponds with gravitational energy, which is the energy stored of an object, due to a vertical height or position. Gravitational potential energy is the greatest at the highest point. In this question, the top of the hill before the red arrow is the highest point on the hill, making it the greatest.