A student conducts an investigation measuring the rate of water loss in milliliters for
three plants. Plant I is exposed to high humidity. Plant 2 to high temperature, and
Plant 3 to room temperature. Measurements are taken at half-hour intervals for three
hours. In planning this investigation, what additional element is needed to ensure that
it has an effective control?
A. Plant I should also be exposed to high temperature.
B. Plant 2 should be exposed to low humidity.
C. Plant 3 should be exposed to normal humidity.
D. All three plants should be in a well-lit environment.