Sam wished to investigate how fertilizer run-off affects the growth of algae in freshwater lakes and streams. He set his experiment up in this way. He placed
900 ml of water into each of five 1000 ml glass beakers. To each beaker he
added 5 ml of water from an aquarium which contained a large concentration of
algae. The beakers were placed under a grow light which was timed to provide 12
hours of light each day. Liquid fertilizer was added to the beakers in the following
amounts: Beaker A - 8 ml fertilizer, Beaker B - 6 ml fertilizer, Beaker C - 4 ml
fertilizer, Beaker D - 2 ml fertilizer, and Beaker E - no fertilizer. Each week a
random sample from each of the beakers was examined under a microscope to
get a count of the number of algal cells present. Which of the following is the
control group for this experiment?