B
Eventually, the Nazis took over many of those parts of Europe.
“i would like to do that again”
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'.
I'm not 100% sure but I believe the answer is B.
