Answer: d. agriculture
Coral reefs are the marine ecosystems. Many aquatic floral and fauna species inhabiting in coral reefs. Being a marine ecosystem it requires sunlight, oxygen, clear water, appropriate temperature ranges, nutrient availability to sustain life of organisms inhabiting. But human activities threaten coral reefs. Agriculture will have an indirect impact on coral reef. Fertilizers used in agriculture may reach coral reefs if the agricultural land is situation near coral reef. Plant growth nutrients present in fertilizers will promote the growth of more number of aquatic plants. This will result in eutrophication which is a condition were water body lacks oxygen making life of inhabiting organism in danger.