Answer: The correct answer is option c. "it is known that participants in research like to present themselves as positively as possible, so students that cheated probably lied and did not report their cheating on the survey".
Explanation: Because everybody wants to present themselves as good student, nobody will want to be identified as a cheat, this will make all the student who participated in the survey to deny of having any intension to cheat or have ever cheated before.
Some student may not want to be frank with the survey, because they are afraid of been identified by the Honor Board of Cheating as one of the student who has once involved or wants to involve in cheating. Nancy can not get an accurate result from such survey because everyone tends to give a positive response in a questionnaire survey.