A self-amplifying reaction and a nuclear explosion in a nuclear power plant are prevented in large part by

A self-amplifying reaction and a nuclear explosion in a nuclear power plant are prevented in large part by:

1. A) the regular addition of uranium-239 to the fuel
2. B) control rods that absorb extra neutrons
3. C) the production of plutonium-239
4. D) fuel rods that absorb tremendous amounts of heat