The answer is c. within the krebs cycle.
Oxygen from the lungs enters the blood through which is transported to every cell of the body. From the cells, carbon dioxide is taken to the blood and transferred to the lungs. Carbon dioxide is produced within the Krebs cycle in the cells. Two reactions of the Krebs cycle give carbon dioxide as product:
1. transformation of D-Isocitrate to α-ketoglutarate,
2. transformation of α-ketoglutarate to Succinyl-CoA.
