A Researcher Was Interested in Studying Stress as It Related

A researcher was interested in studying stress as it related to academic performance incalculus. She also believed that humor reduced stress and might increase academicperformance. She had two classes one hour apart, one at 8 a.m. and one at 10 a.m. onMonday, Wednesday, and Friday. The students self selected into the classes. The researchercollected baseline stress data at the beginning of the semester. In one class she utilized humoron a daily bases and was sure to provide the class with at least one scripted joke or shorthumorous video per day. In the other class, she taught the students as normal with littlehumor, no scripted jokes, and no funny videos. On the day of the midterm, she measuredtheir stress levels before giving the calculus exam. She gave each class the same calculus testand recorded their achievements levels on the exams. Stress was measured using a 10question instrument which summated the 10 questions into one stress construct. Theinstrument had been around for decades and had high reliability and validity measures.
-For the stress/humor scenario which of the following would be true?

A) Stress is an active independent variable
B) Calculus test score is an independent variable
C) Change over time is an independent variable
D) Both calculus score and stress are independent variables