Last year, pharmaceutical manufacturers significantly increased the amount of money they spent promoting new drugs, which they do mainly by sending sales representatives to visit physicians in their offices. However, two years ago there was an average of 640 such visits per representative, whereas last year that figure fell to 501. So the additional promotion must have been counterproductive, making physicians less willing to receive visits by pharmaceutical sales representatives. Which one of the following, if true, most weakens the argument? ['Most pharmaceutical companies did not increase the amount of money they spend promoting drugs through advertising targeted directly at consumers.', 'Most pharmaceutical manufacturers increased the size of their sales forces so that their sales representatives could devote more time to each physician.', "The more visits a physician receives from a pharmaceutical sales representative, the more likely he or she is to prescribe drugs made by that representative's company.", 'Most physicians who agree to receive a visit from a pharmaceutical sales representative will see that representative more than once during a given year.']