In a study to investigate the effect of the color paper (blue, green, orange) on response rates for questionnaires distributed by the "windshield method" in supermarket parking lots, four supermarket parking lots were chosen in a metropolitan area and 10 questionnaires of each color were assigned at random to cars in the parking lots. a. Is this study experimental, observational, or mixed? Why?

b. Identify all factors, factor levels, and factor-level combinations.

c. What type of study design is being implemented here?

d. What is the basic unit of study?