Explain how the farms upriver were adding to the high nitrate levels. (Gizmo)

Farmers were adding high nitrate levels from many large corn farms along the river. ... During the drought, the farmers used extra fertilizer. As rained, the ammonia and nitrate from the fertilizer were washed into the river.

i think the answer would d

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.