Which of the following is an input control over cultural eutrophication? 

A)  planting underwater plants near sewage discharge sites 
B)  putting fences around stockyards 
C)  banning the use of phosphate detergents 
D)  harvesting excess weeds

Cultural eutrophication is caused by an excess of nutrients, especially phosphorus, entering the water system. An input control over cultural eutrophication is banning the use of phosphate detergents, which is a common source of phosphorus in household wastewater. Planting underwater plants near sewage discharge sites can help improve water quality, but it is considered a remedial measure rather than an input control. Putting fences around stockyards and harvesting excess weeds are measures that can help reduce nonpoint source pollution, but they are not specifically targeted towards cultural eutrophication caused by excess nutrients.