Suppose we want to know if a student's GPA is different based on whether they have short or long hair. Perform a two-sample t-test using the "CLASSDATA" dataset in the "DATASETS" folder using the variables, "GPA" and "HairLength." Based on the results, what can we conclude about GPA and hair length?

a. The mean difference in GPA between long and short-haired students equals
b. GPA and hair length are dependent.
c. The mean difference in GPA between long and short-haired students does not equal 0.
d. You can't have a high GPA without long hair.