A person in full protective gear is riding a green dirt-bike ( with the number 108 painted on its side ) on the ridge of a grassy field .
Chances are about even that the person has been riding dirt bikes all his life .
Chances are about even that the person has been riding dirt bikes all his life .
It is almost certain that the person has been riding dirt bikes all his life .
The person has been riding dirt bikes all his life .