The correct option that explains why using the same reaction used in thermonuclear weapons for a nuclear power plant is not possible is:
C) The energy in nuclear fusion can't be generated in a controlled manner.
Nuclear fusion, the reaction that occurs in thermonuclear weapons, releases enormous amounts of energy, but achieving and maintaining the conditions needed for controlled fusion for electricity generation presents significant technical challenges and has not yet been successfully implemented in a practical way. In contrast, nuclear fission, which is used in current nuclear power plants, can be controlled and sustained in a stable manner.