用所给词的适当形式填空。
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. Make sure you _____(recorder) the numbers of tickets you sell.
4. This railway line _____(connect) London to Edinburgh.
5. Scientists think that there _____(be) life on the earth for millions of years.
