Which of the Following Is an Example of an Individual

Multiple Choice

Which of the following is an example of an individual differences (subject) variable?

A) individuals randomly assigned to one of three different treatments in a diabetes study
B) an independent variable involving three levels of nicotine in a smoking cessation program
C) a law enforcement training program compared over a 4-week or an 8-week period
D) individuals classified as introverted or extraverted in a study of alcohol use