We know the earth is a planet．There are seven other planets，and they go  1 the sun together．The eight planets and the sun are2 the solar system．The first planet，3   the sun，is Mercury(水星)．It is 58 miIlion  4  from the sun．Venus(金星)is the second planetfrom the sun，and  5 planet，the earth，is the third．It is from the sun,and 55  planet,the earth,is the third.It is 2,650 million kilometres from the sun．

    Jupiter(木星)，Saturn(土星)，Neptune(海王星)and Uranus(天王星)are all 6 than the earth，7 Venus，Mars and Mercury are smaller than the earth．

    Animals，trees and humans can only 8  on the earth，because the other planets in our solar system don't  9  air or water．Do any  10planets in   solar systems have life?We don't know about it．