Radiation therapy is used to
a. study reaction mechanisms
c. treat cancer
b. detect elements
d. initiate neutron activation analysis

C) Treat Cancer

Explanation: Radiation therapy can be simply defined as a type of cancer treatment where high energy radiations such as x-rays are been used to kill or eliminate cancer cells. In this treatment, the high energy radiation are focused on the affected region, the radiation destroys the cancerous cells in the region all though some healthy cells might also be affected too because of intensity of the radiation.

So radiation therapy is used to treat cancer.