ANS:C - a combination of both nuclear fission & fusion.

A combination of both nuclear fission and fusion can occur in certain types of thermonuclear weapons, commonly known as hydrogen bombs or H-bombs. These weapons are designed to utilize a two-stage process, involving both fission and fusion reactions, to achieve a significantly more powerful explosion than either process alone. Here's how the combination typically works:

1. Fission Stage: The first stage of a hydrogen bomb involves a traditional nuclear fission reaction, similar to that which occurs in atomic bombs. In this stage, a conventional fission bomb (often made of uranium or plutonium) is used as a trigger. The detonation of the fission bomb generates an intense burst of high-energy neutrons.
2. Fusion Stage: The high-energy neutrons produced in the fission stage induce fusion reactions in a secondary stage of the bomb. This secondary stage contains isotopes of hydrogen, typically deuterium and tritium, which are highly reactive and can undergo fusion under extreme temperature and pressure conditions. The fusion reactions release a tremendous amount of energy, much more than the fission reactions alone.
3. Synergy: The energy released from the fusion reactions in the second stage is further amplified by the heat and pressure generated by the initial fission explosion. This creates a powerful, multi-stage explosion that is significantly more destructive than either a pure fission or pure fusion bomb.