Respiratory system I think. I MAY BE WRONG.
Hope I helped!
Answer:

Explanation:
Total distance of one lap of the marathon = 42.2 km
Distance of the lap that is inside the stadium = 400 m
The distance that is run outside the stadium is the difference between the two distances

The distance that is run on the road outside is
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B) Brain...spinal cord, for some reason I keep ending up on questions you've asked.
You should never re-enter a burning building for belongings, animals, or people. Firefighters do that for you.