Scientists think that there has been life on earth for (million) of years. However, we haven't found life on other planets yet. The earth is a planet and it (go) around the sun. And there are seven other planets (请填恰当的关系代词/引导词) also go around the sun. The sun and its planets (call) the solar system. The solar system is a small part of the universe.
Scientists have launched many spaceships (explore) other planets in the solar system. Some spaceships (去) beyond the solar system. However, no one (discover) any life in space yet.
Why has no one from other planets (send) us a message? Have they tried to send information (给) us? With so many stars in space, are we (孤单),or is there life on other planets in space?
