The answer should be A. It takes a very small amount of mass to produce a lot of energy which is displayed in Einstein's equation E=mc². E is the amount of energy given off when some mass is converted into energy.
E=the energy given off, m=the mass turned to energy (I think this is sometimes referred to as the mass defect), and c=the speed of light. Nuclear reactions do not fallow the law of conservation of mass since some of the mass is converted into energy.
I hope this helps. Let me know if anything is unclear.
