The correct option is D Reduce, Reuse and Recycle.
In order to mantain a clean and natural environment, we must adopt the policy of Reduce, Reuse and Recycle. Many tourists visit places and dispose of waste like plastic covers, bottles, food packets, etc on the ground. This reduces the aesthetic value of a place and also leads to soil degradation. Therefore, we must reduce the use of plastics and other non-bio degradables, re use them for other purposes and recycle the waste. This will help preserve natural beauty of a place.