A study of university students found that those who regularly used a particular study app were much more likely to earn grades in the top 10% of their classes than students who did not use the app. Researchers concluded that the study app significantly improves academic performance.However, critics argue that this conclusion is flawed. Students who are highly motivated to succeed academically are more likely both to use study apps regularly and to devote more time and effort to studying. Thus, motivation rather than the app may primarily explain their higher grades.
Which one of the following, if true, most strengthens the critics’ objection to the researchers’ conclusion?
A. Some students who used the study app regularly said that they found its practice exercises particularly useful.
B. Students who used the study app were more likely than other students to have taken advanced courses in high school.
C. Professors often recommend the study app to students who already demonstrate strong motivation to improve their grades.
D. Students who used the study app spent slightly less time studying from textbooks than students who did not use the app.
E. Some highly motivated students who did not use the study app nevertheless earned grades in the top 10% of their classes.