The correct answer is C. Nuclear power generation plants.
Heavy water is a form of water that contains a higher proportion of the heavier isotope of hydrogen, deuterium, than ordinary water. It is used as a moderator in nuclear reactors to slow down neutrons, which increases the probability of them being captured by uranium-235 nuclei, causing fission.
Hydro-electric power plants use the power of moving water to generate electricity. The water is typically stored in a reservoir behind a dam and then released through a turbine, which spins a generator to produce electricity.
The pharmaceutical industry uses a variety of chemicals to produce drugs. Heavy water is not one of these chemicals.
The fertilizer industry uses a variety of chemicals to produce fertilizers. Heavy water is not one of these chemicals.