Scientists suspect that leakage from sewage systems carrying wastewater from the houses on the lake also contributes to nutrient deposit in the lake. In order to test this hypothesis, what should the scientists do next?
A. Sample groundwater near the sewage systems, testing for phosphate and nitrate content.
B. Measure the chlorophyll levels at many more locations in the lake.
C. Test the nutrients in the drinking water of various houses around the lake.
D. Obtain nutrient content of fertilizer used on residential property.