Scientists think that there has been life for__31_ of years. However we haven’t found life on other planets _32_ . The earth is a planet and it _33__ around the sun. Seven other planets also go _34_ the sun. The sun and its planets are __35  the solar system. The solar system is a small part of our galaxy.
Scientists __36_ lots of spacecraft to look at other planets in the solar system, and some spacecraft have gone __37_ the solar system. However, no one __38_ any life in space yet.
But why has no one from other planets sent us a message ? Have they tried to send _39_ to us ? _40_so many stars in the universe, are we alone, or is there life out there in space ? We don’t know.

Scientists think that there has been life for__31_ of years. However we haven’t found life on other planets _32_ . The earth is a planet and it _33__ around the sun. Seven other planets also go _34_ the sun. The sun and its planets are __35  the solar system. The solar system is a small part of our galaxy.

Scientists __36_ lots of spacecraft to look at other planets in the solar system, and some spacecraft have gone __37_ the solar system. However, no one __38_ any life in space yet.

But why has no one from other planets sent us a message ? Have they tried to send _39_ to us ? _40_so many stars in the universe, are we alone, or is there life out there in space ? We don’t know.

Scientists think that there has been life for__31_ of years. However we haven’t found life on other planets _32_ . The earth is a planet and it _33__ around the sun. Seven other planets also go _34_ the sun. The sun and its planets are __35  the solar system. The solar system is a small part of our galaxy.

  Scientists __36_ lots of spacecraft to look at other planets in the solar system, and some spacecraft have gone __37_ the solar system. However, no one __38_ any life in space yet.

  But why has no one from other planets sent us a message ? Have they tried to send _39_ to us ? _40_so many stars in the universe, are we alone, or is there life out there in space ? We don’t know.

31. A. thousands          B. millions       C. hundreds     D. billion

32. A. already       B. never         C. yet          D. just

33. A. go            B. turn          C. travel       D. goes

34. A. to            B. back          C. around      D. into

35. A. called         B. call           C. calling      D. calls

36. A. send         B. sent           C. have sent     D. will send

37. A. out          B. beyond        C. into         D. up

38. A. discovered  B. discovers     C. has discovered   D. have discovered

39. A. message     B. informations    C. information     D. news

40. A. With        B. Have          C. Use         D. Because

(用所给单词正确形式填空) There are more than _______ (billion) of stars in our galaxy，called the Milky Way，and our Sun is only one of them．