(1) The American ideal of a lush green lawn is borrowed from England, where the cool, misty climate makes it easy to grow grass. (2) In America, however, lawns are an energy-intensive, wasteful, and nonproductive form of landscaping. (3) To begin with, achieving a picture-perfect lawn requires gallons of expensive fertilizer and hazardous pesticides that pollute groundwater and run off into lakes and rivers. (4) In addition, lawn owners often exterminate the insects, moles, and gophers that play a part in the balance of nature. (5) Equally destructive is the constant watering lawns require, often where water is a limited resource. (6) Finally, the lawn must be mowed on a regular basis to give it that green carpet effect, requiring endless output of human and mechanical energy. (7) After all the labor and expense, the final result is a flat carpet that lacks interesting features, wildlife, or edible produce. The sentence that expresses the main idea is: (Choose the number of the sentence. Then click the arrow.)