Why Do "Morning People" Tend to Get Better Grades in School

Multiple Choice

Why do "morning people" tend to get better grades in school than "evening people"?

A) "Morning people" tend to be more intelligent, on average.
B) ​"Morning people" tend to be more motivated, on average.
C) More classes and tests are scheduled in the morning than in the evening.
D) "Morning people" tend to have a more active social life.