Judging from the Brief Descriptions Below, Which One of These

Judging from the brief descriptions below, which one of these four teachers is using a mastery learning approach?

A) Ms.Heung gives examinations in which different students are asked different questions, depending on individual student needs and interests.
B) Mr.Bryant assigns term papers and oral reports rather than in-class examinations.
C) Ms.Carroll uses the highest four of a student's six exam scores to determine course grades.
D) Mr.Dickinson insists that students pass each test at the 80% level before beginning the next unit.