Final answer:
A rock at the top of a pile has gravitational potential energy due to its position. This is the energy that it has the potential to convert into kinetic energy if it falls. Chemical and elastic potential energies are not relevant in this context.
Step-by-step explanation:
The correct answer to this question is A) gravitational potential energy. A rock at the top of a pile has gravitational potential energy because of its elevated position relative to the ground. This type of energy is associated with the potential for an object to do work due to its position in a gravity field. As the rock falls, this potential energy is converted into kinetic energy as it accelerates towards the Earth.
Chemical potential energy is related to the energy stored within chemical bonds, which is not related to the height or position of the rock. Elastic potential energy pertains to objects that can be stretched or compressed, such as springs or elastic bands, which also isn't relevant to the rock's situation. Lastly, 'falling potential energy' is not a recognized form of energy in physics; this is likely a confusion with kinetic energy or gravitational potential energy in the act of falling.