Answer: The correct answer is Option D.
Step-by-step explanation:
Nuclear control rods are defined as the rods which are used in nuclear reactor plants to control the fission rate of uranium and plutonium.
These rods are made up of few chemical elements like boron, silver, indium and cadmium. These rods have the capability of absorbing many neutrons without getting fissioned itself.
Thus, from the above information, the correct answer comes out to be Option D.