Now, it may be difficult to predict the future, but many people believe that we will live on Mars by the year 2100. Our own planet, Earth, is becoming more and more crowed and polluted. Well, what problems will we need to solve before we prepare to go to Mars? First of all, transport should be much better. At present, humans need to spend months going to Mars by spaceship. However, by 2100, spaceship can travel at half the speed of light. It might take us two or three days to get there! Secondly, humans need food, water and air to live. Scientists should develop plants that can be grown on Mars. These plants will produce the food, water and air that we need. However, there is no answer for all the problems now. There is also a problem for us to live on Mars. Mars attracts us much less than the Earth does. This will be dangerous because we could easily jump too high and fly slowly away into space there. We will have to wear special shoes to make ourselves heavier. In some ways, life on Mars may not be better than that on the earth today. Food will not be the same --meals will probably be in the form of pills and will not be as delicious as they are today. Also, space travel will probably make many people feel very uncomfortable. So far, how long will it take us from the earth to Mars by spaceship?
Two or three days. A few days. A few months. A few years.