理工类考试辅导：补全对话Avalanche and Its Safety
An avalanche is a sudden and rapid flow of snow， often mixed with air and water， down a mountainside. Avalanches are 1 the biggest dangers in the mountains for both life and property.
All avalanches are caused by an over=burden of material， typically snowpack， that is too massive and unstable for the slope 2 supports it. Determining the critical load， the amount of over-burden which is 3 to cause an avalanche， 4 a complex task involving the evaluation of a number of factors.
Terrain slopes flatter than 25 degrees or steeper than 60 degrees typically have a low5 of avalanche. Snow does not6 significantly on steep slopes; also， snow does not7 easily on fiat slopes. Human-triggered avalanches have the greatest incidence when the snows angle of rest 1is 8 35 and 45 degrees; the critical angle， the angle at which the human incidence of avalanches is greatest， is 38 degrees. The rule of thumb2 is： A slope that is 9 enough to hold snow but steep enough to ski has the potential to generate an avalanche， regardless of the angle. Additionally3， avalanche risk increases with 10 ； that is， the more a slope is disturbed by skiers， the more likely it is that an avalanche will occur.
Due to the complexity of the subject， winter travelling in the backcountry4 is never 100% safe. Good avalanche safety is a continuous 11 ， including route selection and examination to the snowpack， weather 12 ， and human factors. Several well-known good habits can also 13 the risk. If local authorities issue avalanche risk reports， they should be considered and all warnings should be paid 14 to. Never follow in the tracks of others without your own evaluations; snow conditions are almost certain to have changed since they were made. Observe the terrain and note obvious avalanche paths where plants are 15 or damaged. Avoid traveling below others who might trigger an avalanche.
词汇：
avalanche n.雪崩 trigger v. 引起，激发
snowpack n. 积雪场 incidence n.发生(率)
terrain n. 地形，地势 ski v.滑雪
steep adj.险峻的，陡峭的 complexity n. 复杂性
注释：
1.angle of rest：这里指积雪保持静止的角度。
2.rule of.thumb：指“a broadly accurate principle，based on experience or practice rather that theory”，即“通用法则，经验法则”。
3.Additionally：是一个副词，用来引人新的事实或论点，意为“此外”。
4.backcountry：人烟稀少的地区。
练习：
1. A among B of C to D in
2. A when B that C who D whose
3. A mostly B likely C clearly D surely
4. A are B will be C is D was
5. A weight B form C risk D work
6. A fall B flow C roll D gather
7. A fall B flow C roll D gather
8. A among B between C with D for
9. A thick B thin C flat D rocky