Hello, thank you for taking the time to post your question!
I think that the best answer on Question 1 is going to be (c) actually, because mass is converted into energy is one of the core principles of fission. The idea is that the mass defect is directly converted into energy according to E = mc^2.
Same idea on Question 2 then, mass being converted into energy is one of the core principles of fusion as well … the fundamental reason for the energy release is the conversion of mass into energy.
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)