Mars is a planet. 火星是行星。

　　It is next to the Earth. 它紧邻地球。

　　Its size is about one fourth of the Earth. 它约有四分之一个地球大。

　　Mars is not far from the Earth, but the environment is very different. 火星离地球很近，但环境却大不相同。

　　Beacuse Mars is far from the sun. 因为火星离太阳很远。

　　Mars's average temperature is lower than the Earth. 火星的平均温度比地球要低。

　　Mars does not have water. 火星上没有水。

　　There is no oxygen. 那里也没有氧气。

　　Therefore, there are no living things on Mars at all. 因此，火星上根本就没有生物。