Correct Answer - A
(a) Radiotherapy is exposing tumours//cancer cells to radiations, as from radioactive cobalt `-60`. Radon `-120`, `I -131`. Carbalt `-60` is a source of `gamma-raioactions`. These because cancer cells are more rapidly than others because cancer cells are undifferentiated. However, healthy cells in vicinity of cancer cells are also damaged.
Hence, option (a) is true.