a. I want to be an astronaut. I may go to Mars one day. Maybe I will be as famous as Yang Liwei.
b. Mars is my favourite planet. It’s smaller than the earth"and"it’s a lot colder. I think it’s more interesting than the other planets.
c. We call it the Red Planet because the rocks on Mars are red. When the wind blows, the sky is pink. There isn’t a pink sky on the earth! It’s much more beautiful.
d. Unlike the earth, there aren’t any rivers, mountains or people on Mars.