What is the function of control rods in a nuclear reactor?
make radiation
control steam
make fuel
control reaction rate

The function of control rods in  nuclear reactor is to control reaction rate

Explanation:

Control rods are an essential safety system of nuclear reactors. They are employed in nuclear reactors to maintain the "fission rate of uranium or plutonium". Their structures include chemical components such as boron, cadmium, silver, or indium, that are proficient in assimilating many neutrons without themselves fissioning.They form a fundamental element of an "emergency shutdown system "(SCRAM).A control rod is separated from or included into the reactor core to expand or reduce the reactivity of the reactor (increase or decrease the neutron flux). By the variances of the reactivity the changes of neutron power are delivered. This in turn influences the thermal strength of the  nuclear reactor, the volume of steam produced, and henceforth the electricity is produced.