challenge: What is a notable impact of Nike's Vaporfly shoes on the performance of athletes in major marathons?
  
  A. They have allowed Nike-sponsored athletes to dominate the top spots in the fastest marathon times
  B. They have had no significant impact on the performance of athletes in major marathons
  C. They have resulted in a significant decrease in the number of Nike-sponsored winners
  D. They have led to a substantial increase in the number of Adidas-sponsored winners
  Answer: 