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 option would allow Stella to set up a control group for the experiment?
Answer
A
She should provide mist to each of the plants except one plant to keep the air moist and fertilize the plants.
B
She should give the plants receiving the least CO2 a little more oxygen to compensate for the difference in gases.
C
She should give all the flowers the same amount of water.
D
She should place one flower in a similar container, but not pump carbon dioxide into it.