(1) To non-distance runners, a marathon, which consists of 26.2 miles, may seem like the most torturous thing in the world. (2) But runners are keenly aware of just how far the envelope can be pushed. (3) The best of the best train for ultramarathons, which are races with lengths of 50, 100, or even over 100 miles. (4) Dean Karnazes, known as the "Ultramarathon Man," not only lives to run ultramarathons, he runs to

Which of the following is the main idea of the selection?

A
Sentence 2

B
Sentence 4

C
Sentence 12

D
Sentence 14