![Astronautshavealreadyvisitedthemoonandlivedonspacestati...]( "Astronautshavealreadyvisitedthemoonandlivedonspacestati...")
- 问题详情：Astronautshavealreadyvisitedthemoonandlivedonspacestations.They'veneverbeentoanotherplanet,buttheymightvisitMarssoon.Theastronautswillspendaboutsixmonthstravelingtotheplanet,thenabouttwoyearsontheplanetandaboutsixmonthstravelingbacktotheeart...
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