【单选题】National Parks have more and more visitors each year. In the last ten years the number of campers using the camp sites has more than doubled. Camping as a family vacation has suddenly become extremely...
【简答题】America's National Parks ( Part I ) The National Park Service of the U.S.A. controls more than 77 million acres of land, divided up into 320 park sites of extraordinary variety, the latest covering hu...