2．
完形填空 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．
