[填空题]Mountain climbing is becoming popular sport, but it is also a (36) _______dangerous one. People can fall; they may also become ill. One of the most common dangers to climbers is altitude sickness, which can affect even very (37) _______climbers. Altitude sickness usually begins when a climber goes above 8 000 or 9 000 feet. The higher one climbs, the less oxygen there is in the air. When people don’t get enough oxygen, they often begin to (38) _______for air. They may also feel (39) _______and light-headed. Besides these symptoms of altitude sickness, others such as headache and (40) _______may also occur. At heights of over 18000 feet, people may be climbing in a (41) _______daze（恍惚）. This state of mind can have an (42) _______ effect on their judgment. A few (43) _______ can help most climbers avoid altitude sickness. The first is not to go too high too fast. If you climb to 10 000 feet, stay at that height for a day or two. (44) _______.Or if you do climb higher sooner, come back