Joe and Maria tested how the lack of light affected the growth of a plant. Joe and Maria left pot 1 in a sunny place. They put pot 2 under a cardboard box. In all other ways (such as the temperature and the amount of water and fertilizer given), Joe and Maria treated both plants the same. If Joe and Maria wanted to know how the lack of light affects plants, which is the best explanation for why they left pot 1 in the sun?