The consumer advocate assumes a negative effect of radiation— namely, that irradiation, which creates unique radiolytic products, causes those products to be present in the produce itself. (A) weakens the argument by showing that this assumption is false.

This doesn't weaken the argument. The fact that cancer and other health problems have other causes doesn't mean that radioactive substances and gamma rays don't also cause these issues. Also, (B) doesn’t address the assumption that irradiated foods cause these problems.

The consumer advocate assumes that, just because irradiation can reduce the vitamins in produce, it does reduce the vitamins in produce. (C) weakens the argument by showing that this assumption is false and that irradiation actually keeps the vitamin content intact.

(D) weakens the argument by pointing out a positive effect of irradiation: irradiated foods have fewer harmful chemicals than most non-irradiated foods. It also shows that the assumption that irradiation leaves produce with more harmful chemicals is false.

The consumer advocate assumes that, because irradiation creates unique radiolytic products and these products cause cancer, irradiated foods cause cancer. (E) undermines this link by showing that cancer rates are not actually higher among people who eat irradiated food.