单选题 Unless we spend money to spot and prevent asteroids (小行星) now, one might crash into Earth and destroy life as we know it, say some scientists. Asteroids are bigger versions of the meteoroids (流星) that race across the night sky. Most orbit the sun far from Earth and don"t threaten us. But there are also thousands of asteroids whose orbits put them on a collision course with Earth. Buy $ 50 million worth of new telescopes right now. Then spend $ 10 million a year for the next 25 years to locate most of the space rocks. By the time we spot a fatal one, the scientists say, we"ll have a way to change its course. Some scientists favor pushing asteroids off course with nuclear weapons. But the cost wouldn"t be cheap. Is it worth it? Two things experts consider when judging any risk are: 1) How likely the event is; and 2) How bad the consequences are if the event occurs. Experts think an asteroid big enough to destroy lots of life might strike Earth once every 500, 000 years. Sounds pretty rare—but if one did fall, it would be the end of the world. "If we don"t take care of these big asteroids, they"ll take care of us," says one scientist. "It"s that simple. " The cure, though, might be worse than the disease. Do we really want fleets of nuclear weapons sitting around on Earth? "The world has less to fear from doomsday (毁灭 性的) rocks than from a great nuclear fleet set against them," said a New York Times article. (272 words)

单选题 What does the passage say about asteroids and meteoroids?

单选题 What do scientists say about the collision of an asteroid with Earth?

单选题 What do people think of the suggestion of using nuclear weapons to alter the courses of asteroids?

单选题 We can conclude from the passage that______.

单选题 Which of the following best describes the author"s tone in this passage?