The mayor of Statville had to decide how to allocate her education budget between the two high schools in town, “Stat Sticks” and “Datum High.” To decide which school deserves a bigger portion of the budget, she wanted to assess which school is more helpful to its students.
She went over the grade sheets of the students from both schools in the past 555 years. For each student, she calculated the difference between scores on their high school entrance and exit exams. Then, she compared the average difference for the students from each school.
What type of statistical study did the mayor use?

Is the study appropriate for the statistical questions it's supposed to answer?
Mark the most suitable choice.
Choose 1
Choose 1

(Choice A)
A
No, because she didn't compare the scores with scores in high schools from other towns.

(Choice B)
B
Yes, because the mayor didn’t sample the students, but analyzed the grades of all the students.

(Choice C)
C
No, because the study collects data about entrance exam scores, which are irrelevant.

(Choice D)
D
Yes, because it gives a good measure of the change the students go through in each school.