A man died and went to Heaven. There were thousands of other people there. They were all naked and everyone looked as they did at the age of 21. He looked around to see if there was anyone he recognized. Suddenly, he saw a couple, and he knew that they were Adam and Eve. How did he know?
This is kind of easy and hard at the same time.
So until an answer that is close to the answer, i will not give that clue.