1. Edison is one of the greatest ________ (invent) in the world.
2. The gravity on the surface of Mars is about one ________ (three) as strong as it is on the earth.
3. Six books have been written by her, ________ (include) the story book.
4. This railway line _________ (connect) London to Edinburgh.
5. Scientists think that there _________ (be) life on the earth for millions of years.