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.