Experiments lead the Army to a simple method of overcoming this problem. Scouts (侦察员) ahead of the troops are trained to shake snow from evergreen bushes, creating a dotted line as they cross completely snow-covered landscape. Even the scouts themselves throw lightweight, dark-colored objects ahead on which they can focus too. The men following can then see something. Their gaze is arrested. Their eyes focus on a bush and having found something to see, stop searching 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 continuous white land is overcome.
40. To prevent snow blindness caused by the strong light from snow, wearing glasses or not _________.
A. depends on whether the snow is white enough
B. makes no difference
C. makes much difference
D. depends on whether the snow is thick
41. When the eyes are tired, tears flow out __________.
A. to clear the vision
B. to make the eyes stop searching
C. to make the vision unclear
D. to produce more and more liquid
42. Snow blindness can be prevented by ___________
A. moving one's gaze back and forth
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