A cell phone company is trying to find a waterproof cell phone case to add to its product line. Company managers know that plastic and silicone will be used. They also know that the depth of the water—less than five feet, between five feet and 20 feet, and more than 20 feet—affects the waterproof case. An experiment will compare all combinations of these choices. The cell phones will be subjected to each treatment, with one group dropped in water without a case, and all phones will be scored for quality. What is the control? a. Cell phones in the plastic case
b. Cell phones in the silicone case
c. Cell phones in the plastic case dropped in water less than five feet deep
d. Cell phones in the silicone case dropped in water more than 20 feet deep
e. Cell phones with no case