10.None of them has an environment with air, so people and things cannot grow.
11.The sun and its planets are called the solar system.
12.The stars (we see at night )are the suns in other solar systems.
13.They are a long way away and their light has travelled for many years to reach us.
14.It’s hard to understand how large the universe is.
15.But why has no one (from other planets) sent us a message?
16.I haven’t read anything (as good as that) for a long time!
17.It’s so good that I have asked the library to keep the next book for me.
