题目

Growing trees in the concrete jungle of Los Angels brings neighbors benefits beyond beauty.     As the  36  of TreePeople, a nonprofit organization he founded in 1973, Andy, now 54, has inspired hundreds of thousands of volunteers to  37  plant more than two million trees throughout Southern California.        Tree People 38 tools, blueprints, planting demonstrations, and tree-care supervisors free to all the participants,  39  me. “You will need their support,” Andy said, referring to my neighbors. “ 40  the community behind you, the trees you plant will die in five yea图中数码代表不同的山脉，其中属于地势阶梯分界线的是（　　） A、①②B、②③C、③④D、①④