Dr. Jennings is doing a study on the experience of being a racial minority on a college campus. He goes to the Asian Student Association, Black Student Union, and Hispanic Student Group on his campus to recruit participants for his study. Dr. Jennings only includes Asians, African-Americans, and Hispanic participants in his study. What type of sampling is Dr. Jennings using?
Select one:a. systematic samplingb. cluster samplingc. quota samplingd. purposive sampling