Answer:
b Fuel for fusion reactors can be extracted from ocean water.
Step-by-step explanation:
The fuel is deuterium, which makes up 0.02% of the hydrogen atoms in water. The oceans contain more than a billion cubic kilometres of water, so that's a lot of deuterium.
a is wrong. The fuel for fusion reactors is deuterium.
c is wrong. There is much research, but there are no large-scale fusion reactors in operation.
d is wrong. Fusion reactors do not produce radioactive waste as spent fuel. Most of the radioactive waste would be the reactor core itself.