Some people believe humans could live on the planet Mars (火星) by the year 2100.     1    (hopeful), people could start all over again and build    2    better world on Mars. Here is    3    life there could be like. With the    4    (develop) of technology, the journey might only take about 20 minutes by 2100 in spacecraft that travel at the speed of light!    5    , the spacecraft would travel so fast that the journey might be quite    6    (comfortable). Humans cannot survive     7    water, oxygen (氧气) or food. Nobody    8    (know) whether there would be enough water or oxygen on Mars for people there. Gravity could be another problem. The gravity (重力) on Mars    9    (be) only about three-eighths (八分之三) of that on the Earth (地球). People would have to wear boots that are specially designed to prevent    10     (them) from floating off into space. Life on Mars would be interesting as well as challenging.