At a charter high school, administrators wish to collect a sample of 50 students. The proportions of the student body represented by each class are:
45% freshmen, 28% sophomores, 16% juniors, and 11% seniors. They decide to randomly sample 23 freshmen, 14 sophomores, eight juniors, and five
seniors. Which of the following methods was used to select the probability sample?


a) replication
b) systematic
c) stratified
d) cluster
e) simple random sample