Veterinarians generally derive some of their income from selling several manufacturers' lines of pet-care products. Knowing that pet owners rarely throw away mail from their pet' s veterinarian unread, one manufacturer of pet-care products offered free promotional materials on its products to veterinarians for mailing to their clients. Very few veterinarians accepted the offer, however, even though the manufacturer's products are of high quality. Which of the following, if true, most helps to explain the veterinarian's reaction to the manufacturer's promotional scheme? ['Veterinarians sometimes recommend that pet owners use products formulated for people when no suitable product specially formulated for animals is available.', 'Many pet owners have begun demanding quality in products they buy for their pets that is as high as that in products they buy for themselves.', "The special promotional materials were intended as a supplement to the manufacturer's usual promotional activities rather than as a replacement for them.", "The manufacturer's products, unlike most equally good competing products sold by veterinarians, are also available in pet stores and in supermarkets."]