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閱讀下面的短文，然后根據短文內容，在每小題所給的四個選項中選出最佳選項。
Space travel is nothing new．The first spacecraft with a human was sent up into space in 1961．
Since then, people have not only traveled to space, but many of them have also lived there in space stations for some time．
The Soviet Union(前蘇聯)sent the first space station into space in 1971．This space station was called Salyut I．Salyut I was designed as a place where people could live while they observed space and did experiments．The first group of astronauts lived there for 23 days．The Soviet Union went on to make seven more Salyut space stations．At about the same time, the United States built its own space station, called Skylab．
Astronauts visited and often lived in these space stations for a short time．However, it wasn't until the late 1980s when the Soviet Union sent the Mir space station that people began to live in space for a longer time．Mir stayed in space from 1989 until 2001, when it was decided that the space station was too old and no longer safe to live in．
Living in apace stations seems to be fun, but astronauts face many problems．One of them is food．All the meals on space stations are put together on Earth and sent there by space shuttle．Because the food has to last a long time(sometimes up to three months), a lot of it has to be stored in cans．The space station does not have a fridge, but it has a cool room to keep fruit and vegetables fresh．Astronauts also eat many other foods such as dried meat that do not need special care．
Without the help of gravity, sitting down to eat can be tough．Astronauts sometimes have to fix themselves to the wall while eating．They also have to be very careful to that food does not float away．
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