题目选项分析

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?

【选项】Most of the veterinarians to whom the free promotional materials were offered were already selling the manufacturer's pet-care products to their clients.