Medical columnist: Some doctors recommend taking vitamin C to help maintain overall health because vitamin C is an antioxidant, a substance that protects the body from certain types of oxygen particles that can trigger disease. People suffering from various ailments are encouraged to take vitamin C to guard against developing other health problems. However, doctors are now discouraging some cancer patients from taking vitamin C, even when they are undergoing therapies with side effects that are detrimental to their overall health. Which one of the following, if true, most helps to explain why the doctors' recommendation to some cancer patients differs from the general recommendation regarding vitamin C? ["Certain side effects of cancer therapies that are detrimental to patients' overall health are not affected by vitamin C.", 'Cancer cells that are susceptible to certain types of cancer therapies are not likely to be affected by the presence of vitamin C.', "Vitamin C has not been shown to reduce people's risk of developing cancer, even at the very high dosage levels recommended by some doctors.", 'Some kinds of cancer cells absorb large amounts of vitamin C, which interferes with the oxidation mechanism by which many cancer therapies kill cancer cells.']