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     From mountains to oceans to deserts, Earth is filled with awesome beauty. A__1__ we suffer from

typhoons or earthquakes sometimes, we humans have a pretty fantastic home. It's hard to i__2__

anyone wanting to leave.

    Still, some scientists think that l_3_ Earth is a necessary part of humanity's future. Stephen Hawking,

a well-respected p__4__, once said he didn't believe mankind would be able to s_5_ the next thousand

years if it didn't spread into space. "There are too many accidents that can take people's lives on a single

planet." Hawking said. "But I'm an optimist. We will reach out to the stars." In the past few d__6__,

humans have taken important steps toward conquering space. Astronauts have walked on the moon,

and space t_7__ have caught wonderful images of distant galaxies. The International Space S __8__

has even given astronauts the opportunity to stay in space for months. But there is a big d_9_ between

staying in space for a short time and living there p__10___.