C is the slowest of the runners, but starts at a position ahead of A and B when the starting gun is fired, so C is in the lead for a while.
A and B both start from the starting line when the starting gun is fired. A is faster than B. So A is the first to pass C, and A stays in the lead after that.
After a short while, B also passes C.
After that, C remains last on the track.