二. 根据 Act.2 课文完成下列短文填空。 Though scientists think that there has been life on the earth for 1. of millions of years, we have not found life on any other 2. in the solar system.Our solar system is a 3. part of the Galaxy.Scientists have also 4. many other galaxies 5. the universe. They are so far away that it is 6. to imagine how large the universe is.Scientists have 7. spaceships to the planet Mars and 8. the solar system. 9. , no spaceship has travelled far 10. to reach other stars in our Galaxy.