Science departments need a way to ensure that only those students most committed to being science majors will receive passing grades in introductory science courses. Some of the students in the very demanding introductory science courses who are most enthusiastic about science do not receive passing grades in those courses. None of the students in the very demanding introductory science courses who are least enthusiastic about science are among the students most committed to being science majors. Introductory science courses should not continue to be designed to serve as proving grounds if doing so has not served its intended purpose.
Professor: Many introductory undergraduate science courses are intended to be "proving grounds, " that is, they are designed to be so demanding that only those students most committed to being science majors will receive passing grades in these courses. However, studies show that some of the students in these very demanding introductory courses who are least enthusiastic about science receive passing grades in these courses. Hence, designing introductory science courses to serve as proving grounds has not served its intended purpose.
Which one of the following is an assumption that the professor's argument requires?