单项选择题

Passage Two Questions 46 to 50 are based on the following passage.
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 hunters, hikers (徒步旅行者), fishermen, or woods workers who are careless in disposing of their smoking materials. The Forest Service has posted rules in many of the National Forests that prohibit smoking except in certain designated 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 hazardous areas.
The most important natural cause of fire is lightning (闪电). This accounts for 11 percent of forest fires on protected land for the entire nation. In the Western States, lightning causes a much higher percentage of fires than it does in the East. 　　
Advances in knowledge of fire weather are helping forest protection forces to know when to be alert to lightning-caused fires. Adequate and well-equipped forces can control them quickly and hold the damage to a minimum. Experiments in “seeding” thunder clouds to prevent or control the lightning itself have been in process for many years, but new breakthroughs are needed for any significant reduction in the fires lightning starts.

This passage is chiefly about （）

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