The makers of Activite, a natural dietary supplement, claim that it promotes energy and mental alertness. To back up their claim, they offer a month' s supply of Activite free to new customers. Clearly, Activite must be effective, since otherwise it would not be in the company' s interest to make such an offer. Which one of the following, if true, most weakens the argument? ['The makers of Activite charge a handling fee that is considerably more than what it costs them to pack and ship their product.', 'The mere fact that a dietary supplement contains only natural ingredients does not insure that it has no harmful side effects.', 'The nutrients in Activite can all be obtained from a sufficiently varied and well-balanced diet.', 'There are less expensive dietary supplements on the market that are just as effective as Activite.']