Hello,
The answer is option C "26.2 miles".
Reason:
The owners of the marathon would not put it over that specific length of the race because you dont want to push those people harder and make them run longer. They do this so the participants wont get injured or a health injurie such as a heat stroke wont take place so they wont get sued. Therefore the answer is option C.
If you need anymore help feel free to ask me!
Hope this helps!
~Nonportrit