What invention do you think was the most helpful to the World?

I think, that mobile phone was the most helpful invention to the world. The person, who invented it was Dr Martin Cooper. He wanted to create something new, something that can be helpful in communications between people. He succeeded in 1973, when he became the general manager of Motorola's Communications System Division. He made the first call on a mobile phone, in the streets of New York.
People were astonished with this idea and everyone wanted to have it. Regrettably, in those times, there weren't many mobiles and they were expensive, too. Later mobiles became cheaper and more people could afford them. In our times, nearly everyone has got a mobile phone. It makes life more comfortable, modern, secure, etc. Mobiles are very useful for us when we have a problem, when we are in a critical or hopeless situation. Sometimes mobiles can save life, e.g. when we are witness of an accident, we can call an ambulance. We can ring our family, friends whenever we want, too. It is faster method of communication than writing letters. In modern mobiles there are many additions. They have a music player, a camera, a voice recorder, an internet, etc. Mobile is very handy, because it is small and light. A lot of people can't work without mobiles, they're essential.
Life is much easier with a mobile. Mobiles helped many people in the world. That's why I think that mobile phone is the most helpful invention to the world.