Final answer:
None of the options provided (layers, bangs, or undercut) are standard subsections for a classic square one-length haircut below the shoulders. This haircut typically involves cutting hair evenly around the head without layering or texturizing.
Step-by-step explanation:
When cutting a square one length below the shoulders haircut, the types of subsections usually taken are determined based on the desired end result of the haircut. Since the options provided are layers, bangs, and undercut, none would be considered standard subsections for a classic one-length haircut. A one-length haircut is characterized by cutting the hair to the same length all the way around the head, generally without layering or significant texturizing. Subsections for cutting might be based simply on dividing the hair into manageable sections to ensure an even cut, rather than any distinct style elements like layers or bangs.