9. An experiment is described below. A student was interested in comparing sunblock lotions, which contain chemicals that protect the skin from sunburn. The student purchased three different brands of lotion at three different prices and performed an experiment to see which one best protected the skin. The lotions cost $3, $5, and $7 for an 8-ounce bottle. The sun protection factor (SPF) was 30 for all three lotions. The student applied equal amounts of each lotion next to each other on one of her arms. The three areas covered by the lotions were the same size. The student observed the three areas for color change after two hours of Sun exposure. Identify two conditions that were held constant in this experiment. There are three.​