Many people believe the glare from snow causes snow blindness. Yet, 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 United States 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(荒芜的)snow-covered landscape. 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, the eyes never stop searching and the eyeballs become sore and the eye muscles ache. Nature offsets this irritation by producing more and more fluid which covers the eyeball. The fluid covers the eyeball in increasing quantity until vision blurs(模糊), then is obscured(使变模糊), and the result is total, even though temporary, snow blindness.
Experiments 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 cross 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(急走)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.

单选题 When the eyes are sore, tears are produced to ______.

单选题 Snow blindness may be avoided by ______.

【正确答案】 C

【答案解析】 细节理解题。根据文中第三段的内容可以知道，军队中有一种简单的方法解决雪盲症：将常绿灌木上的雪摇晃下来，常绿灌木形成了一条线；或是将一些深色、重量轻的物体扔在地上，这样他们就可以使自己的视线有可以停留的地方。因此要避免雪盲症，需要让眼睛有可以聚焦的地方。因此选项C正确。

单选题 The scouts shake snow from evergreen bushes in order to ______.

【正确答案】 A

【答案解析】 细节理解题。根据文中第三段的内容可以知道士兵们将常绿灌木上的雪摇晃下来，是为了让身后的人有东西可以看。A项正确。B项“美化风景”，C项“使他们在寒冷中得到温暖”，D项“帮助那些迷路的人”均与其实际原因不符。

单选题 A suitable title for this passage would be ______.

【正确答案】 A

【答案解析】 主旨大意题。这篇文章通篇讲的都是雪盲症及其解决办法。第一段介绍了一直以来人们对于雪盲症产生原因的错误观点；第二段介绍了美国军队纠正雪盲症产生的真正原因；第三段讲的则是雪盲症的解决办法。因此答案为A项。B项“雪盲症的自然治愈方式”只是原文第二段中提到的一个细节：眼睛对于不断搜索目标的一种自然反应。C项、D项均未提到文章的中心“雪盲症”。

单选题 The eyeballs become sore and the eye muscles ache because ______.

【正确答案】 D

【答案解析】 细节理解题。根据原文第二段第四句“Finding nothing, hour after hour, the eyes never stop searching and the eyeballs become sore and the eye muscles ache”可以知道，眼睛找不到聚焦的地方，就不断地搜索目标，而这就导致了眼球和眼部肌肉的疼痛。因此D项正确。