At the end of the year, Wilson' s Department Store awards free merchandise to its top salespeople. When presented with the fact that the number of salespeople receiving these awards has declined markedly over the past fifteen years, the newly appointed president of the company responded, "In that case, since our award criterion at present is membership in the top third of our sales force, we can also say that the number of salespeople passed over for these awards has similarly declined. " Which one of the following is an assumption that would allow the company president's conclusion to be properly drawn? ["Wilson's calculates its salespeople's sales figures in the same way as it did fifteen years ago.", "Policies at Wilson's with regard to hiring salespeople have not become more lax over the past fifteen years.", "The number of salespeople at Wilson's has increased over the past fifteen years.", "The criterion used by Wilson's for selecting its award recipients has remained the same for the past fifteen years."]