阅读理解 The two things-snow and mountains-which are needed for a ski area are the two things that cause avalanches(雪崩), large mass of snow and ice crushing down the side of a mountain-often called 'White Death.' It was the threat of the avalanche and its record as a killer of man in the western mountains that created the snow ranger. He first started on avalanche control work in the winter of 193738 at Alta, Utah, in Wasatch National Forest. This mountain valley was becoming well known to skiers. It was dangerous. In fact, more than 120 persons had lost their lives in 1936 and another 200 died in 1937 as a result of avalanches before it became a major ski area. Thus, development of Alta and other major ski resorts in the west was dependent upon controlling the avalanche. The Forest Service set out to do it, and did, with its corps (团队)of snow rangers. It takes many things to make a snow ranger. The snow ranger must be in excellent physical condition. He must be a good skier and a skilled mountain climber. He should have at least a high school education, and the more college courses in geology, physics, and related fields he has, the better. He studies snow, terrain, wind, and weather. He learns the conditions that produce avalanches. He learns to forecast avalanches and to bring them roaring on down the mountainsides to reduce their killing strength. The snow ranger learns to do this by using artillery(炮), by blasting with TNT, and by the difficult and skillful art of skiing avalanches down. The snow ranger, dressed in a green parka which has a bright yellow shoulder patch, means safety for people on ski slopes. He pulls the trigger(扳机) on a 75 mm. Recoilless rifle(无后坐力步枪), skis waist deep in powder testing snow stability, or talks with the ski area's operator as he goes about his work to protect the public from the hazards(危险)of deep snow on steep mountain slopes. 1. The snow rangers are employees of ________. A. the Forest Service B. the Resource Bureau C. the Tourist Board D. the Sports Bureau 2. A snow ranger himself must be ________. A. a college graduate B. a physicist C. a geologist D. a mountaineer 3. A snow ranger uses very powerful guns________. A. to warn skiers of an approaching avalanche B. to signal for help in an emergency C. to create an avalanche D. to communicate with the ski area's operator 4. The primary duty of the snow ranger is ________. A. to make sure ski area's operators are following safety rules B. to predict and control avalanches in mountainous areas C. to check skis and repair them D. to forecast the weather