2. 外语
  3. Many people believe the glare from snow causes snowblindness. Yet, dark glasses or not, they find themselves 【C1】______headaches

Many people believe the glare from snow causes snowblindness. Yet, dark glasses or not, they find themselves 【C1】______headaches

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问题     Many people believe the glare from snow causes snowblindness. Yet, dark glasses or not, they find themselves 【C1】______headaches and watering eyes, and even snowblindness, when【C2】______ to several hours of "snow light".
    The United States Army has now determined that glare from snow does not cause snowblindness in troops in a snow-covered country.【C3】______, a man’s eyes frequently find nothing to focus on in a broad【C4】______ of barren snow-covered terrain. So his gaze continually shifts and jumps back and【C5】______ over the entire landscape【C6】______ something to look at. Finding nothing, hour after hour, the eyes【C7】______stop searching and the eyeballs become 【C8】______ and the eye muscles ache. Nature【C9】______ this irritation by producing more fluid which covers the eyeball. The fluid covers the eyeball in increasing【C10】______until vision blurs, then is【C11】______, and the result is total, even though temporary, snowblindness.
    Experiments【C12】______ the Army to a simple method of overcoming this problem. Scouts【C13】_____ of a main body of troops are trained to shake snow 【C14】______evergreen bushes, creating a dotted line as they cross completely snow-covered landscape.【C15】______ the scouts themselves throw lightweight, dark colored objects ahead on which they too can focus. The men【C16】______ can then see something. Their gaze is 【C17】______. Their eyes focus on a bush and having found something to see, stop 【C18】______the snow-blanketed landscape. By focusing their attention on one object 【C19】______,the men can cross the snow 【C20】______becoming hopelessly snowblind or lost. In this way the problem of crossing a solid white terrain is overcomed.
【C19】
选项 A、at times
B、at a time
C、at any time
D、at no time
答案B
解析 短语辨析题。句意为：通过每次只关注一个目标……。at times“间或，有时”；at a time“每次”；at any time“在任何时候”；at no time“从不，决不”，所以[B]at a time符合原文意义。
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