Researchers recently found that people who bought passes to individual fitness classes showed up 99 percent of the time, while those bought a package of five passes in advance only showed up 25 percent of the time. One explanation is that the more aware a gym patron is about the cost of a pass, the more likely that patron is to use it.
Which of the following would, if true, best serve as an alternative explanation of the results of the study?
【选项】
Those who attended all five classes became eligible to win a gift certificate.
选项是否正确？