Stella wants to test the hypothesis “If carbon dioxide levels increase, the growth rate of sunflowers will increase.” She places five young sunflower plants into similar containers and sets up pumps that release different amounts of carbon dioxide into each container. She plans to measure the daily height of the plants for two weeks and graph the data. Which additional considerations would produce the most reliable experimental results?

A. She should also provide mist to each of the plants to keep the air moist and fertilize the plants. She should record her data in a bar graph for easy analysis.

B. She should increase her sample size to 50 plants and place them all in the same area. The plants receiving less CO2 should be given a little more water.

C. She should be sure to give all the flowers the same amount of water. She should make observations twice a day for four weeks for better results.

D. She should place one flower in a similar container, but not pump carbon dioxide into it. She should also give each plant the same amount of water.