Many people believe the glare from snow causes snowblindness. Yet, dark glasses or not, th

Many people believe the glare from snow causes snowblindness. Yet, dark glasses or not, they find themselves suffering from headaches and watering eyes, and even snowblindness, when exposed 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. A man's eyes frequently find nothing to focus on in a broad expanse of barren snow-covered terrain(地域). So his long look continually moves and jumps back and forth over the entire landscape in search of something to look at. Finding nothing, hour after hour, the eyes never stop searching and eyeballs bee sore and the eye muscles ache. Nature offers this disfort by producing more and more liquid which covers the eyeball. The liquid covers the eyeball in increasing quantity until vision became not clear, and then is not easily seen and the result is total, even though not very long, snowblindness.
Experiments led the Army to a simple method of solving this problem. Scouts, ahead of a main body of troops, are trained to shake snow from evergreen bushes creating a dotted line as they cross pletely 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 eyes focus on a bush and have something to see. By focusing their attention on one object at a time, the men can cross the snow without being hopelessly snowblind or lost. In this way the problem of crossing a solid white terrain is solved.
1. The first paragraph is mainly concerned with     .
A. need for dark glasses      
B the whiteness from snow
C. headaches, watering eyes and snowblindness 
D. snow glare and snowblindness
2. According to the author, recent work on snowblindness shows that it is caused by     .
A. exposure to bright light
B. failure to focus on an object
C. a loss of vision which doesn't last long
D. focusing on dark colored objects for a very long time
3. Suppose you walk across a pletely snow-covered area, what should you do to solve the problem of snowblindness?
A. By wearing dark sun glasses.
B. By throwing an extra pair of black shoes ahead.
C. By asking the Army for help.
D. By walking backwards.
4. A suitable title for this passage would be     .
A. Snowblindness and How to avoid it     B. Soldiers in Snow　　
C. Nature's Cure for Snowblindness       D. Snow VisionD