Scientists think that there has been life on Earth for millions of years.However,we haven't found life on other planets yet.Why not?
The Earth is a planet and it goes around the Sun.Eight other planets also go around the Sun.None of them has an environment with air,so people and things cannot grow.The Sun and its planets are called the solar systemThe solar system is a small par of our galaxy.
But scientists have discovered many other galaxies in the universe.They are a long way away and their light has travelled for many years to reach us.It is hard to understand how large the universe is.
Scientists have sent lote of spacecraft to look at other planets in our solar system,and some spacraft have gone beyond the solar system.However,mo ome has discovered any life in space yet.
But why has no one from other planets sent us a message?Have they tried to send information to us?With so many stars in the universe,are we alone,or is there life out there in space?We don't know...yet.
參考答案:科学家们认为在几百万年前地球上就有生命了。然而，我们还没有在其他的行星上发现生命。为什么呢？
地球是个行星，绕太阳运行。其余八个行星也绕太阳运行。它们都没有大气层，因此人和其他生物不能生存。太阳和它的行星叫做太阳系。太阳系只是银河系的一小部分。
但科学家们发现宇宙中还有其他的星系。它们距离我们很遥远，它们发出的光要经许多年才能到达地球。我们很难知道宇宙到底有多大。
科学家们发送出许多飞行器去探测太阳系的其它行星，有些飞行器飞出了太阳系。然而，还没有一只飞行器在太空中发现任何生命。
但是为什么没有外星人给我们发来信息呢？他们试图给我们发过信息吗？宇宙中有那么多星星，我们却是孤单的，或者在太空以外有生命存在吗？我们还不知道。
