carol is doing a science fair project for her science class. she wants to investigate how the amount of water given to a plant affects its growth. she tests 30 plants and is careful to record how much water each plant gets. she also controls the type and amount of soil in each pot and the number of seeds in each pot. she uses 1 cup of water each day for her control group, giving 1 cup of water to ten plants and she gives 2 cups of water to ten plants, and 3 cups of water to ten plants. whe it is time to present her project, she concludes that the plants getting 3 cups of water a day grew better than the control group that received 1 cup of water a day or the plants receiving 2 cups of water each day. which additional piece of information is most important to include if someone wants to reproduce carol's experiment