[单项选择]Heat exhaustion is a condition caused by ______ to sunlight or another heat source which often results in dehydration and salt depletion.
A. a reaction to
B. overexposure
C. an limitation of
D. an absence of

Most forest fires are caused by human carelessness or ignorance. Forest fire prevention, therefore, is mainly a problem of creating better understanding of the importance of forests, an awareness of the danger of fire in the woods, and a sense of personal responsibility to safeguard the forests from danger. This is not an easy job.
Careless smokers are responsible for thousands of forest fires each year. Many of these are started when cigarette butts(烟蒂 )and matches are thrown from automobiles. Others are caused by hunter, hikers(徒步旅行 ), fishermen, or woods workers who are careless in disposing of their smoking materials. The Forest Service has posted rules in many of the National Forest that prohibit smoking except in certain designated (指定的) areas. Many of the states have laws against throwing lighted materials from automobiles. The prevention of smoker-caused fires, however, depends upon changing the attitudes and behavior of millions of people who smoke in haz
A. holding the fire damages to a minimum
B. people who have changed their attitude and behavior
C. enough rue fighters with good fire-fighting devices
D. carrying out experiments in "seeding" thunder clouds