When a swimmer dives underwater and holds her breath, her body's oxygen supply becomes limited. To continue producing ATP during this anaerobic condition, her cells will most likely undergo lactic acid fermentation.
Lactic acid fermentation allows cells to convert glucose into ATP when oxygen is scarce, producing lactic acid as a byproduct. This process is particularly common in muscle cells during intense exercise when oxygen can't be delivered fast enough to meet energy demands.
So, the correct response is:
lactic acid fermentation