The answer is B. natural gas
Answer:

Explanation:
<u>Gravitational Potential Energy</u>
It's the capacity of an object to do work due to its relative height from a fixed reference point.
It's computed as
GPE=m.g.h
Where m is the mass of the object, h is its height and g is the acceleration of gravity, 
The mass of water is given as

The height above the rocks is h=50 m. Let's compute the GPE


It should be expressed in scientific notation

The GPE at the bottom, where h=0

The change of gravitational potential energy is:

