Which plant type remains completely submerged in water?

The selected answer is correct because submersed plants are specifically adapted to live completely underwater. They have specialized structures that allow them to thrive in aquatic environments without rising above the water's surface. These plants can photosynthesize underwater and often play a crucial role in providing habitat and oxygen for aquatic life.

Emergent plants, in contrast, typically grow in water but have stems and leaves that extend above the water level. Floating-leaf plants have leaves that float on the surface while their roots remain submerged. Free floating plants also float on the surface of the water but do not have roots anchoring them to the substrate below. Therefore, these types do not maintain their entire structure beneath the surface like submersed plants do.