1、 Similar machines have flown in space aboard NASA's shuttles, but they couldn't be tested for long enough to prove whether they were effective.
类似的机器也曾搭乘美国宇航局的航天飞机在太空中飞行，但无法进行时间足够长的测试来证明它们是否有效。
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2、 A bus shuttles passengers back and forth from the station to the terminal.
一辆公共汽车在火车站和公共汽车终点站之间往返运送旅客。
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