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According to paragraph 3, what was the position of the opponents of the "'protectionist' hypothesis"? A. Extrafloral nectar provides plants with a direct defense against attack by insects. B. Ants substantially benefit plants that secrete extrafloral nectar. C. The secretion of extrafloral nectar plays a role in the plant's internal functioning. D. Ants visit plants that secrete extrafloral nectar as often as they visit plants that do not.