Tony Is About to Participate in His First 10K Run

Tony is about to participate in his first 10K run. One of his friends told him to make sure to "carbo load" and to take a niacin supplement before the race. Tony had heard the term "carbo loading" before but was not sure why it was necessary and had n why he would need a niacin supplement. He had been training for months and was confident that he would finish the race ea therefore, did not heed his friend's advice.
On the day of the race, Tony was so excited it felt like he was flying through the first half of the race. Tony wanted to beat his current best time and was nearing the end of the race when he decided to pick up his pace to the finish line. Unfortunately, Tony became fatigued and had to walk to the finish line out of breath and with his muscles burning.
-Refer to Scenario 3.1. Tony was breathing heavily but still able to walk to the finish line. Why?

A) Tony was breathing heavily because he was trying to get enough oxygen to his tissues to start producing ATP again in large amounts. He was still able to walk because, even though he lacked oxygen at the end of his electron transport chain, he was still producing a small amount of ATP via glycolysis.
B) Even though he had used all of his energy, he was able to produce a small amount of ATP via gluconeogenesis. However, the effort to do so caused him to breathe heavily.
C) Tony was breathing heavily because he needed to release the heat generated through metabolism. Because he was overheated, he had to walk.
D) Tony was breathing heavily because he was trying to get enough oxygen to his tissues to start producing ATP again. He was able to walk because he still had enough oxygen getting to his brain to keep him conscious.
E) None of the answers is correct.