Answer: c. high-level waste
Step-by-step explanation:
The used or spent fuel comes from the nuclear reactor that can be no longer efficient to be used again for the purpose of generating electricity, because the efficiency to conduct fission reaction by such fuel is low. But still it may be thermally hot, highly radioactive and harmful. It comes under the category of high level wastes. The high level wastes are those wastes that are produced as a byproduct of the nuclear reactors.