第5部分：补全短文（第46～50题，每题2分，共10分）
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Should the U.S. halt human apace flight?
The Columbia accident has revived the debate on whether the rewards of human space exploration are worth the risks No. I was a teacher when men first landed on the moon in 1969, and I remember how it moved my students and this country. （46） And we haven't ventured outward since then. That's 30 years too long! America's human space-flight program is adrift, with no clear vision or goals beyond the completion of the International Space Station.
I want NASA to establish a phased series of goals over the next 20 years, including human visits to asteroids that cross the Earth's orbit, establishing a research and living facility for humans on the moon, and human expeditions to the surface of Mars and its moons. （47）
An astronaut is today's Christopher Columbus, who sailed into the unknown and discovered the Americas. The knowledge we gain from having actual people exploring can never be replaced by robots. （48） Robots are useful, but humans can do things that robots can't.
The real obstacle we face in overcoming the drift in the nation's human space-flight program is not technological and it's not financial. （49）
The lesson from the Columbia accident is not that humans don't belong in space. （50）
