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 down to a lower height when you sleep.
Also, drink plenty of liquids and avoid tobacco and alcohol.
(45) _______. You breathe less when you sleep, so you get less oxygen.
The most important warning is this: if you have severe symptoms and they don’t go away, go down! (46) _______. 36（）