What is the invention that has benefited mankind the most?

There are many answers to this question and it is all down to your opinion. for example some people may say that guns have benefited mankind the most but i disagree and think that they should never have been invented.

My answer to this question is the invention of the usage of fuels because without fuels we would not have things such as electricity and without this the internet, computers phone etc would all be useless and if e could not use fuels so would cars and planes.