iron rods

cadmium rods

graphite rods

brass rods

cast iron

beryllium

steel

boron

fission of radioactive materials

fusion of radioactive materials

burning of the fuel rods in oxygen

none of these

to absorb the excess neutrons

to increases the energy of the neutrons

to slow down the neutrons

none of these

CANDU type reactors

boiling water reactors

pressurized water reactors

gas cooled reactors