Answer:
it needs to be in the right context. What context/purpose are you trying to do this for? Is it for a job interview or sth?
Explanation:
There is only one answer included here, and even that is incomplete. What are our choices?
The t-shirt that they give only to people who finish is a big reason that so many people take up the challenging race.
This paraphrase presents the same information as in the sentence, but since it should be a bit more of a summary, it takes out the specific detail of how many people actually run the race, which can just be paraphrased into 'so many'.