Which of the following should be included in a watershed map to best determine the non-point source of a pollutant, such as fertilizer, found in a river?

A. The total volume of groundwater in the aquifer
B. The total area and the average yearly precipitation of the watershed
C. The land use upstream of the river and water quality indicators in streams that run downstream into the river
D. The total volume of surface water of the river and the land use downstream of the river