Which step of glycolysis would stall if no fermentation pathway were available in the absence of oxygen?

1. Various methods of fermentation ensure an adequate supply of the oxidized carrier for the sixth step in glycolysis. 2. The sixth step is the one that loads high-energy electrons onto that carrier. 3. Without these pathways that step would not occur. 4. If the sixth step stops, no adenosine triphosphate would be harvested from the breakdown of glucose at all. 5. The first step spends adenosine triphosphate rather than making it, so it is not the carrier-dependent bottleneck. 6. The tenth step depends on the substrate reaching it, which it cannot do once step six has stalled. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 7 "Cellular Respiration", section 7.5 Metabolism without Oxygen_