A researcher studying the habits of business school students found that, on average, students on academic probation due to low grade point averages tend to cheat more often than do other students. The researcher concluded that students who cheat are likely to receive poor grades, even if they are not caught cheating. Which of the following, if true, most seriously weakens the researcher's conclusion?

a. Students who are placed on academic probation due to low grade point averages often resort to cheating as a way to improve their grades.
b. Some students with high grade point averages frequently cheat in order to obtain good grades.
c. Not all students who cheat get caught.
d. Some students on academic probation do not cheat.
e. Students who cheat in school are also likely to engage in other dishonest behavior.