Students in Mr. Painter's science class studied samples of pond water using a microscope. To prepare for the experiment, the students placed a drop of pond water on each microscope slide, and then covered the drop with a cover slip that was marked with a 1 mm grid. Using the microscope to view the slides, students counted how many of each type of organism they found in each 1 mm square. Finally, each student calculated the total number of each type of organisms. Their data is shown below. Which organism is the least plentiful in the pond water studied? A. amoeba B. volvox C. euglena D. paramecium