From a Nuclear Fission Standpoint, Which of the Following Best

From a nuclear fission standpoint, which of the following best describes a chain reaction?

A) Fission of one nucleus releases neutrons which induce fission in another nucleus.
B) Chains of atoms undergo fission one after another in a rapid sequence and release large amounts of energy.
C) Radioactive material reaches a critical mass and then releases large amounts of radiation at once.
D) Small lighter elements combine together in a chain to form single heavier nuclei.
E) None of the above.