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In an experiment, 90 newborn flies are divided evenly into three separate
groups and placed in boxes inside an incubator that is maintained at a
constant temperature of 30°C. On a daily basis, the first group is given water
containing 1 mg/mL of sugar; the second is given water containing 2 mg/mL
of sugar; and the third is given water containing 3 mg/mL of sugar. After four
weeks, the average length of the flies in each group is determined.
Which factor is the independent variable in this experiment?
A. Number of flies in a group
B. Average length of flies in a group
C. Concentration of sugar in the water
D. Temperature of the incubator