The study reassuringly suggests that astronomers already know the location of more than 90 percent of the very largest asteroids — the huge planet-busters that could cause mass extinctions.
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但火山爆发不是历史上最大的杀手-这个名称属于小行星,也就是很小的行星。
But volcanoes aren't history's greatest killers - that title goes to asteroids, that is, minor planets.