During nuclear fission, great amounts of energy are produced from
a. very small amounts of mass.
b. tremendous amounts of mass.
c. a series of chemical reactions.
d. particle accelerators.

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.