A class of eight students measured the population of water fleas living at the edge of a large pond. This is the method each student used. 1. Put
some pond water in a white tray.2.Take a pond net and scoop at the edge
of the pond a few times.3.Empty the pond net into the water in the
tray.4.Count the number of water fleas in the tray. The photograph below
shows a student working. The students did not control some variables. Give
two variables the students should have controlled to make this a valid
method.