Students filled two beakers with 500 mL of water each. They placed three drops of live algae culture into each of the beakers, then used a dissolved oxygen sensor to measure the oxygen content of the water in each beaker. The students then stirred 5 mL of nitrogen-rich fertilizer into one of the beakers, and labeled the beaker A. Nothing was added to the second beaker, which the students labeled B. Both beakers were placed under a high-intensity light over a weekend. On Monday, the students measured the amount of oxygen in the water of each of the beakers. Which aspect of the watershed were these students trying to model? A. The effect of fertilizer-contaminated surface water flowing as runoff into a waterway

B. How stagnant or non-flowing water can result in providing a habitat for living organisms such as algae

C. The inverse relationship between water, light, oxygen, and photosynthesis

D. How light and oxygen levels in water affect the growth of algae within a system over time