This topic reminds me of a film released recently which was based on the famous old story happened in the Tang dynasty. At that time, the queen really liked eating one kind of furits called litchi. She lived in the capital city Changan, but litchi grew in the tropical area which was 2000 kilometres aways from the capital. In order to let the queen eat the freshest fruit, a group people created a lot of ways of keeping the fruit fresh. They eventually succeeded. So, if you let me choose the greatest invention, maybe my answer is fridge and plane. If they have this two kinds of inventions, they wouldn't be that tired to delivery fresh fruit from long distance aways. New inventions appear every day. Human beings keep changing this world we live in. More and more inventions will be created in the process of figuring out the problems which confuse us.