Expound on why fusion is more beneficial than fission as a nuclear energy source in terms of availability and hazard. Despite its prospect as an almost inexhaustible energy source, explain why fusion reactors have not been developed yet.

• A. In terms of availability, hydrogen isotopes are naturally occurring in very large amounts in seawater while uranium is not naturally occurring. In terms of the hazard, fusion products are less polluting than fission products. Fusion reactors have not been developed yet because the temperature required for the reaction is extremely high and is impossible to reach.
• B. In terms of availability, both deuterium and tritium are naturally occurring in very large amounts in the Earth's crust while uranium is not naturally occurring. In terms of the hazard, all fission and fusion products are radioactive, but fusion products are somehow less polluting. Fusion reactors have not been developed yet because there are not many countries willing to invest in the tapping of nuclear fusion.
• C. In terms of availability, hydrogen isotopes used as fuel for fusion are cheaper and more available than uranium fuel. Both fuels are naturally occurring but uranium fuel still has to be enriched. In terms of the hazard, fusion products are non-radioactive and non-polluting in the long term, unlike fission products. Fusion reactors have not been developed yet because of the very high temperatures required and the lack of an efficient device to achieve this and give a practical energy output.
• D. In terms of availability, hydrogen isotopes used as fuel for fusion are naturally occurring, unlike uranium. In terms of the hazard, fusion products are non-radioactive and non-polluting in the long term, unlike fission products. Fusion reactors have not been developed yet because, at present, not many countries take part in fusion research and investment was not enough to prime the perfect conditions for practical nuclear fusion reactors.

Answer: (C)