Travis sets up an experiment to determine the growth of sunflowers are affected by the application of a specific fertilizer. He places the same amount of seeds and the same amount of soil in pots, and then places the pots outside in a sunny location. Of the 20 pots, 10 contain fertilizer and 10 do not receive fertilizer. Travis waters all of the pots with the same amount of water, twice each week. What is the control in Travis' experiment?
A) the amount of water
B) the type of seeds used
C) the seeds with fertilizer
D) the seeds without fertilizer