Arash Wants to Examine the Relationship Between Stress and Eating

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 an advantage of the type of study Arash performed

A) It is easy and fast to perform such a study.
B) You can get a lot of detailed information about the participants.
C) You can establish causal relationships between variables.
D) Any change in the dependent variable is entirely due to the independent variable(s) .