A PhD Student in Education Wants to Study the Relationship

A PhD student in Education wants to study the relationship between the time spent studying and the grade received. He obtains research funding and recruits 30 students each in three majors. He then randomly assigns each student to study 0.5 hours, 1 hour, 1.5 hours, or 2 hours per day for the subject. At the end of the semester, he should do the following with the data:

A) plot numerical grade received against time studied.
B) calculate averages for each time group and, if different, declare that time studied determines grade received.
C) look at variability in grades received. If students in different time groups have the same grade, he should conclude that there is no relationship between time studied and grade received.
D) None of the answer options is correct.