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.
-What is the independent variable in Arash's study

A) The participants' gender.
B) The participants' eating habits.
C) The task difficulty.
D) How many Timbits the participant eats.