Use the following information to answer the question. Calvin and Michelle wanted to test the effects of different household cleansers on the growth of mildew. They selected three identical bathroom tiles to use in their experiment. To one tile, they applied Brand X cleanser. To another, they applied Brand Y cleanser. The third tile did not receive any cleanser. They observed the growth of the mildew over a period of four days. Their results are shown in the table below. Growth of mildew Date Brand X cleanser Brand Y cleanser No cleanser Area (mm2) Area (mm2) Area (mm2) 05/18/11 0 0 0 05/19/11 0 0.25 0.50 05/20/11 0 1.0 1.25 05/21/11 0.20 2.75 3.0 Which of the following is a constant, or control, in this experiment? A. the results observed over four days B. the brand of cleanser that worked best C. the use of identical bathroom tiles D. the brand of cleanser that didn’t work