1. A primary difficulty in energy production by fusion is
(a) The scarcity of necessary fuel.
(b) The disposal of radioactive by-products produced.
(c) The high temperatures necessary to overcome the electrical repulsion of protons.
(d) The fact that it is possible in volcanic regions only.
2. If two hydrogen nuclei, each of mass fuse together and form a helium nucleus of mass
(a) mHE < 2mH,
(b) mHE = 2mH,
(c) mHE > 2mH,
(d) All of the above are possible.