Cliff wants to determine whether people prefer red apples or green apples. In order to obtain good results, he decides to conduct this survey at a car festival. Out of the 5000 people who attended the festival, Cliff surveys 10 attendees randomly. The survey reads, "Which do you prefer, red apples or green apples" Seven of ten people surveyed answer that they prefer red apples. From his survey, Cliff concludes that most people prefer red apples. Cliff's results may not be reliable because of problems with his study?