The best answer is D. A way where humans do not have direct impact to the coral reefs is agriculture. The other choices have a clear direct impact to the colas since they are activities that involves the bodies of water where the coral reefs are found. Agriculture, on the other hand, is based on the land therefore humans do not have direct contact to the reefs. However, this has still an effect on the coral reefs when the nutrients run off to the sea where it may result nutrient loading.