Pick up the energy-yielding process of glycolysis:

Explanation

The correct answer is the oxidation of PGAL. In glycolysis, PGAL undergoes an oxidation reaction where it donates electrons to NAD+, forming NADH. This step is crucial as it leads to the formation of 1,3-bisphosphoglycerate (1,3-BPG), which later participates in substrate-level phosphorylation to generate ATP. The reduction of PGAL is incorrect, as PGAL is oxidized, not reduced. Phosphorylation of PGAL does occur, but it is not the direct energy-yielding step; it prepares the molecule for energy extraction. The reduction of 3-PG is also incorrect, as 3-PG is not reduced in glycolysis; it is a product formed after the oxidation of PGAL.