An Experiment Compares Student GPAs Between Those Who Eat Breakfast

Multiple Choice

An experiment compares student GPAs between those who eat breakfast and those who don't. After the experiment, it is found that those who eat breakfast in the cafeteria are also listening to music. Not only do the two groups differ in terms of who has breakfast, but they also differ in terms of who hears the music. Music is a:

A) random variable
B) possible confounding variable
C) an error
D) an independent variable