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  3. Air turbulence can substantially accelerate the appearance of large droplets triggering rain by presenting a new mechanism,

Air turbulence can substantially accelerate the appearance of large droplets triggering rain by presenting a new mechanism,

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问题          Air turbulence can substantially accelerate the appearance of large droplets
     triggering rain by presenting a new mechanism, the "sling effect", which
     increases collisions of droplets that have become detached from the airflow.
Line  First, vapor condensation in cloud cores produces small droplets resembling one
(5)   another in size, which then expand to raindrop size by coalescing under the
     effects of air turbulence—a force thought to cause collisions of similar-sized
     droplets whose radii exceed a few micrometers. Then, turbulent vortices act as
     small centrifuges that spin heavy droplets out, creating concentration
     heterogeneities and jets of droplets, both of which increase the mean collision
(10)  rate, which in turn accelerates rain initiation.
         One can conclude that rain prediction requires a quantitative description of
     droplet collision in turbulence, a mechanism which helps meteorologists to
     forecast rainfall,  but detailed understanding of the phenomenon entails
     consideration of such factors as warm and cold fronts stretching over hundreds
(15)  of miles, individual clouds perhaps a mile or so across, and even, as the
     mechanism illustrates, tiny eddies perhaps a few centimeters or so in size.
According to the passage, air turbulence generally does which of the following? Ⅰ. Creates small droplets of equal size to form in cloud cores. Ⅱ. Causes different concentrations of rain droplets to form in different places. Ⅲ. Speeds up the rate by which large droplets appear.
选项 A、Ⅰ only
B、Ⅱ only
C、Ⅰ and Ⅱ only
D、Ⅱ and Ⅲ only
E、Ⅰ,Ⅱ, and Ⅲ
答案D
解析
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