In an experiment, a scientist adds half a cup of fertilizer to pond “A” and zero fertilizer to pond “B” to compare the amount of algae growth from the fertilizer over a 30-day period. Each day he records the amount of algae that has grown in pond "A" and in pond "B" . Measuring the amount of algae that grows would represent a(n)

A. dependent variable
B. independent variable
C. prediction
D. model