12.Every student will have a computer at home (connecting to an inter-planet computer network.)

10.The gravity on Mars is only about three-eighths of the gravity on Earth.

　★11.There will be many different designs for settlers to choose from.

9.However, it is not sure if these plants could produce water.

8.Humans need food, water and air to survive.

7.By 2100, the journey might take only a very short time in space shuttles (that travel at half the speed of light.)

6.At present, our spacecraft are too slowly to carry large numbers of people to Mars-it takes months.

5.Our planet, Earth, is becoming more and more crowded and polluted.

4.It may be difficult to imagine.

3.Daniel is thinking about what life will be like in the future.

2.I thought you liked Mars. 我原以为你喜欢火星。