题目内容：
阅读下文，回答题。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 low _5_____ of avalanchE．Snow does not_6________ significantly on steep slopes; also, snow does not _7______ easily on flat slopes.
Human-triggered avalanches have the greatest incidence when the snow’s angle of rest is_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 thumb 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．Additionally, 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 backcountry is never 100% safE．Good avalanche safety is a continuous_11_________, including route selection and examination of 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.
请在1处填写正确答案。 A．among
B．of
C．to
D．in
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