The First 10 Students Who Arrived for the Friday Lecture

The first 10 students who arrived for the Friday lecture filled out a questionnaire on their attitudes toward the instructor.The first 10 who were late for the lecture were spotted,and afterward filled out the same questionnaire.The appropriate design for testing the significance of the difference between the means is

A) related samples t-test.
B) independent samples t-test.
C) one-sample t-test.
D) z-test.