MOUNTAIN CLIMBING One of the most difficult but rewarding of pastimes is the sport of mountain climbing. Mountain climbing can be divided into two categories, rock climbing and ice climbing, and the modern climber must【B1】______ many different skills. Rock climbing 【B2】______ a combination of gymnastic ability, imagination and observation, but perhaps the most necessary skill is being able to 【B3】______ out how much weight a padicular rock will 【B4】______ Mountaineers climb in groups of three or four, each climber at a distance of approximately six metres from the next. Usually one person climbs while the other climbers 【B5】______ hold of the rope. The most experienced climber goes first and 【B6】______ the other climbers which 【B7】______ to go. When the leader has reached a good position, he or she makes the rope secure so that it is【B8】______ for the others to follow. Since much mountain climbing 【B9】______ place in bad weather, snow skills 【B10】______ a very important part. Ice axes are used for 【B11】______ steps into the snow, and for testing the ground. Climbers always tie themselves 【B12】______ so that, if the leader does fall, he or she can be held by the others and 【B13】______ back to safety. The number of dangers 【B14】______ by climbers is almost endless. Yet perhaps the most difficult part of the sport is the physical effort needed when the air has little oxygen. The 【B15】______ of oxygen can leave mountaineers continually out of breath. 【B1】______