LIFE is from Birth to Death (B to D) but in between B and D is C. What is C?

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They say life is commence from Birth to Death, from the day we were born life starts until the day we demise/die on this world. But some relevant questions traveled on my mind questioning how the letter in between by B & D plays a role in our existence on this world? What is the importance of this letter C, and what if we will extend to letter D? How this letter stands for our life in this world? Could you extend your opinions how this letters C & D represents to the events transpired of our life related to our existence on this earth?