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

highly enriched uranium as fuel and light water as moderator and coolant

natural uranium as fuel and heavy water as moderator and coolant

enriched uranium as fuel and ordinary water as moderator and cooler

only fertile material