Answer
Runner A won the race.
Yes, all the runners finished the race.
Runner B was running quite quickly but probably fell. After a couple of seconds, he or she was able to resume running and managed to get second place.
Work Step by Step
One can see that runner A got the quickest time to reach 100 meters.
All runners finished the race because they reached 100 meters.
At some interval, one can see that there is a slope of zero, indicating that runner B didn't move for a couple of seconds.