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 ____51____ 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 ____52____ supports it. Determining the critical load， the amount of over-burden which is ____53____ to cause an avalanche， is a complex task ____54____ the evaluation of a number of factors.
Terrain slopes flatter than 25 degrees or steeper than 60 degrees typically have a low ____55____ of avalanche. Snow does not ____56____ significantly on steep slopes； also， snow does not ____57____ easily on fiat slopes. Human-triggered avalanches have the greatest incidence when the snow‘s angle of rest is ____58____ 35 and 45 degrees； the critical angle， the angle ____59____ which the human incidence of avalanches is greatest， is 38 degrees. The rule of thumb is： A slope that is flat enough to hold snow but steep enough to ski has the potential to generate an avalanche， regardless of the angle. Additionally， avalanche risk increases with ____60____； 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 backcountry is never 100% safe. Good avalanche safety is a continuous ____61____， including route selection and examination to the snowpack， weather ____62____， and human factors. Several well-known good habits can also ____63____ the risk. If local authorities issue avalanche risk reports， they should be considered and all warnings should be paid ____64____ 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 ____65____ or damaged. Avoid traveling below others who might trigger an avalanche.
51 A among B of C to D in
52 A when B that C who D whose
53 A mostly B likely C clearly D surely
54 A about B include C involving D contain
55 A weight B form C risk D work
56 A fall B flow C roll D gather
57 A fall B flow C roll D gather
58 A among B between C with D for
59 A at B of C in D on
60 A use B time C snow D rain
61 A journey B trip C fact D process
62 A conditions B reports C forecast D event
63 A increase B reduce C improve D remove
64 A price B effort C attention D money
65 A missing B grown C big D fresh