Final answer:
Gamma Radiation (C) is the type of nuclear radiation commonly used to treat cancer, though research on alpha and beta radiation is ongoing.
Step-by-step explanation:
The type of nuclear radiation that can be used to treat cancer is Gamma Radiation (C). Other types of radiation, such as alpha and beta radiations, have also been researched for use in cancer treatment, but gamma radiation and X-rays are more commonly used. Radiation therapy involves using high-energy radiation to damage cancer cells' DNA, effectively killing them or preventing them from dividing. This can be done externally through external beam radiation therapy or internally via brachytherapy.