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  3. Many people believe the glare from snow causes snow blindness. Yet, wearing dark glasses or not, they find themselves suffering

Many people believe the glare from snow causes snow blindness. Yet, wearing dark glasses or not, they find themselves suffering

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问题     Many people believe the glare from snow causes snow blindness. Yet, wearing dark glasses or not, they find themselves suffering from headaches and watering eyes, and even snow blindness, when exposed to several hours of "snow light".
    The Canadian Army has now determined that glare from snow does not cause snow blindness in troops in a snow - covered country. Rather, a man’s eyes frequently find nothing to focus on in a broad expanse of barren snow - covered terrain. So his gaze continually shifts and jumps back and forth over the entire landscape in search of something to look at. Finding nothing, hour after hour, they eyes never stop searching and the eyeballs become sore and the eye muscles ache. Nature offsets this irritation by producing more fluid which covers the eyeball. The fluid covers the eyeball in increasing quantity until vision blurs, then is obscured, and the result is total, even though temporary, snow blindness.
    Expriments led the Army to a simple method of overcoming this problem. Scouts, ahead of a main body of troops, are trained to shake snow from evergreen bushes, creating a dotted line as they corss completely snow - covered landscape; even the scouts themselves throw lightweight, dark colored objects ahead on which they too can focus. The men following can then see something. Their gaze is arrested. Their eyes focus on a bush and having found something to see, stop scouring the snow - blanketed landscape. By focusing their attention on one object at a time, the men can cross the snow without becoming hopelessly snow blind or lost. In this way the problem of crossing a solid white terrain is overcome.
To prevent headaches, watering eyes and blindness caused by glare from snow, dark glasses are
选项 A、indispensable
B、ineffective
C、useful
D、ease the irritation
答案B
解析 细节理解题。根据第一段提到“wearing dark glasses or not，they find them—selves suffering from headaches and watering eyes，and even snow blindness，when exposed to several hours of‘snow light’”，戴不戴眼镜都会产生“雪盲”的症状，如眼疼、流泪甚至雪盲，故选B项。
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