Which you think it is the most useful invention of the humanity of the history ?

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And which do you think it will be the most useful invention in the future ? In my opinion the most useful invention it was the aeroplane that allowed people to travel around long distances and to send postals that arrive in a short period of time at foreign countries ( compared with 150 years ago, that all comercial movements between two countries were to slowly because it was no aeroplane )