The correct answer to the question is : Nuclear fusion.
Nuclear fusion is the thermonuclear reaction in which light unstable nuclei will fuse with each other to form heavy stable nuclei with the release of energy.
This energy is released due to the mass defect.
Photosynthesis, anaerobic respiration are the life processes where gamma rays can not be emitted.
Similarly photoelectric emission results no gamma radiation. In this process, electrons are emitted from the surface of the metal when light of suitable frequency falls on it.
Hence, the correct answer is nuclear fusion where gamma energy is produced due to radioactive process.
In short, Your Answer would be Option D
Hope this helps!
also a particle and an anti particle annihilation creates gamma rays.
not too sure thinking it will always be directed towards the centre of the earth. could be wrong not sure