According to a University of Florida researcher, the longer a beachgoers sits in wet sand or stays in the water, the higher the risk of gastroenteritis (University of Florida News, Jan. 29, 2008). The result is based on a study of over 1,000 adults conducted at three popular Florida beaches. The adults were divided into three groups: (1) beachgoers who were recently exposed to wet sand and water for at least two consecutive hours, (2) beachgoers who were not recently exposed to wet sand and water, and (3) people who had not recently visited a beach. Suppose the researcher wants to compare the mean levels of intestinal bacteria for the three groups. For this study, identify each of the following:

a. Experimental unit

b. Response variable

c. Factor

d. Factor levels