Arash Wants to Examine the Relationship Between Stress and Eating

Multiple Choice

Arash wants to examine the relationship between stress and eating when someone is on a diet. He recruits an equal number of male and female participants to respond to a questionnaire about their eating habits, their typical mood, and their overall anxiety levels. Arash ensures half of his male participants and half of his female participants are on a diet and the other half are not. After the questionnaire, all participants are randomly assigned to complete one of two tasks. Half of the participants solve a difficult math problem in front of a group of math professors within a certain time limit. The other participants solve a simple arithmetic problem in a waiting area alone, with no time limit. After they perform the task, all participants are asked to complete one more questionnaire about their stress level while sitting next to a box of Timbits. Arash tells the participants to help themselves to the Timbits, and secretly counts how many Timbits the participant actually eats.
-Which of the following is NOT likely to be a confounding variable in Arash's experiment

A) The gender of the participants
B) The math skill of the participants
C) The dietary restrictions of the participants
D) The shyness level of the participants