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Unless we spend money to spot and stop asteroids (小行星) now, one might crash into Earth and destroy life as we know it, say some scientists. Asteroids are bigger (36) of the meteoroids (流星) that (37) across the night sky. Most orbit the sun far from Earth and don’t (38) us. But there are also thousands of asteroids whose orbits put them on a (39) course with Earth. Buy $ 50 million (40) of new telescopes right now. Then spend $10 million a year for the next 25 years to (41) most of the space rocks. By the time we (42) a fatal one, the scientists say, we’ll have a way to change its course. Some scientists favor (43) asteroids off course with nuclear weapons. But the cost wouldn’t be cheap. Is it worth it (44) . Experts think an asteroid big enough to destroy lots of life might strike Earth once every 500,000 years. (45) . "If we don’t take care of these big asteroids, they’ll take care of us," says one scientist. "It’s that simple." (46) "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.