Great questions. The feature that I wish to add to the human body would be the wings - to fly high in the sky. The problem we have in this dynamic world is getting enormous day by day. The problem of Pollution, traffic Jams/congestions, global warming is just increasing and there is no stoppage there. No doubts measure are being taken to control all these situations but they are sufficient that we can curb them fully.
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The only solution I see and given an opportunity to add a new feature to the human body than it would be the WINGS. Wings will solve all this problem listed to a great extent and would make commutation easy as well. Imagine how fun it would be if we could fly. So, definitely having WINGS is something I would wish to be added to the human body