Final answer:
Usain Bolt tripped after winning the 200m gold in 2015 due to a cameraman on a Segway losing control and bumping into him.
Step-by-step explanation:
The cause of Usain Bolt tripping immediately after winning the 200m gold in 2015 was b) A man on a Segway. Bolt had just finished his victory lap when a cameraman on a Segway lost control and accidentally drove into him. Despite the incident, Bolt was not seriously injured and was able to laugh it off afterwards.