Explain why evolution by natural selection can not occur if there is no variation in a characteristic

Why can cancer in the lymph nodes (lymphoma) be particularly dangerous? a. the lymph node's ability to produce cancer-fighting lymphocytes would be compromised. b. the lymph node's ability to produce cancer-fighting lymph would be compromised. c. the lymph nodes produce lymph, which nourishes growing cancer cells. d. the lymph nodes produce chyle, which nourishes growing cancer cells.