Why is lactic acid the end product of fermentation and not the PYRUVATE molecule?

Well the main difference would be that lactic Fermentation doesn't use oxygen while the Pyruvate cycle does

Explanation:

Lactic Fermentation is Anaerobic Respiration

The cycle that uses Pyruvate is Aerobic Respiration

answer; i believe is(b)converging

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.