Question

a photo needs to be edited so that its background almost disappears. which of these features should be altered?
transparency/opacity
number of layers
feathering
anti-aliasing

Explanation:

Transparency/opacity controls how visible an element (like a photo background) is. Increasing transparency (lowering opacity) makes the background fade or almost disappear. Layers control image stacking, feathering softens edges, and anti-aliasing smooths jagged edges, none of which directly make a background nearly invisible.

Answer:

transparency/opacity