What is the greatest invention of all time and why?

            The greatest invention of all time is cell phones! They are useful because people would know where you were at all times. They are also useful when there is an emergency. Such as if there was someone in your house (robber, killer, Chucky (The doll that kills people.) etc.) and you were hiding in your bathroom (where there is no phone.) you can call for help.
           They are also useful for social purposes. If you want to hang out with a friend you can just whip out your handy dandy cell phone and text them and ask. I use my phone for homework too. For instance if I don't know an assignment I can just text a friend and ask for it. Cell phones are a great innovation for people of all ages. It takes a little time to get used to but it is always useful in the end!