Ada and Elijah have decided to do an experiment testing how sunlight affects plant growth. The students choose the same type of plants, soil, pots and amount of water they give the plants. They also make sure each plant is put in their designated area for the same amount of time each day. One plant is placed outside; one in front of a window that only gets light for 1/2 the day, and one in a closet. The students collect data every day for two weeks. Their results show that the plant outside grew the most and the plant in the closet had the least amount of growth. What are the constant variables that Ada and Elijah used in their experiment?