In each of the following scenarios, determine whether the data is paired or not paired. Part A: Compare pre- (beginning of semester) and post-test (end of semester) scores of students.
Part B: Assess gender-related salary gap by comparing salaries of randomly sampled men and women.
Part C: Compare artery thicknesses at the beginning of a study and after 2 years of taking Vitamin E for the same group of patients.
Part D: Assess effectiveness of a diet regimen by comparing the before and after weights of subjects.