In a nuclear power plant control rods are used to a. speed up the reaction. b. slow down the reaction. c. feed material to the reaction. d. stabilize the walls of the nuclear reactor.

speed up the reaction.

slow down the reaction.

Explanation:

Control rods are used in nuclear reactors to control the fission rate of reactions. Their compositions includes certain elements such as boron, cadmium, silver, or indium, which are capable of absorbing many neutrons without themselves fissioning.

Control rods may be inserted into a nuclear reactor core to reduce the reaction rate or withdrawn to increase it depending on the desired rate of reaction.