How does the energy released in a nuclear reaction get created?

A. By an endothermic reaction occurring

B. By the mass of the nucleus getting smaller

C. By bonds being created between two atoms

D. By water turning into hydrogen and oxygen

In a nuclear reaction energy is released when large atoms are split. During the process the total (relativistic) energy is conserved, but the "missing" rest mass reappear as kinetic energy released in the reaction. So, according to this the energy release in a nuclear reaction get created by bonds

being created between two atoms.