How many genes are needed to control a single-gene trait? A. two B. millions C. one​

one. A single gene trait is controlled by one gene, its in the name :)

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.