What about this riddle can you figure it?

Mark and Billy have been the best friends ever since they were little kids.


They are also very competitive. Throughout the years they have challenged each other to do both physical and mental challenges. And they completed the challenge.





But one day Mark thought of something to challenge Billy to do - something he could start but never finish. The average man could do it and so could Mark and they were both the same sex and the same size. It is a physical challenge.





Can you figure out what it was?What about this riddle can you figure it?
Mark challenged Billy to get a tan, but he couldn鈥檛鈥illy is an albino.What about this riddle can you figure it?
Mark challenged Billy to grow older than himself
Mark challenged Billy to get a tan, but he couldn鈥檛鈥illy is an albino!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Mark challenged Billy to get a tan, but he couldn鈥檛鈥illy is an albino.


seen this one be4!
Mark had to hike a wall but Billy had no legs!! hey it could be anything c'est injuste!!!
a family?
A Car!!!
Would it be a friendship?