A、Nobody was injured in it. B、It was caused by an error. C、It killed 27 miners. D、It affected national electricity supply. B新闻开篇

U.S. government health and safety officials are investigating the cause of the recent explosion at a West Virginia coal mine, which killed 12 miners. [3]The accident was apparently an error in an industry which has prided itself on miner safety at a time of extraordinary expansion. Mine companies operate in 27 states, from West Virginia in the east to Montana in the west, producing a total of about one billion tons a year, or more than a third of the world’s coal supply. The U.S. economy is dependent on coal production.
    Coal-fired power plants generate about 50 percent of the nation’s electricity. More than half the nation’s coal is mined underground by thousands of men and women who daily risk injury and death. [4]But the occupation has become much safer since the late 1960s, when the U.S. Congress passed laws requiring federal mine inspections.
3. What do we learn about the recent explosion at a coal mine?
4. What made the mining industry safer in the late 1960s?