From which of the following structures does a flatworm expel solid waste?

cloaca

vesicle

pores in skin

mouth

A flatworm expels solid waste through the structure known as mouth.

Flatworms only have one digestive opening, meaning that their mouth also serves as their anus - there is a single opening through which they eat and expel unnecessary materials.

Flatworms don't have a cloaca and vescile, and pores are too tiny to expel solid waste through them.