The correct answer is C. Profundal.
The profundal zone is the deepest part of a lake, where there is little or no light. This means that there is very little photosynthesis taking place in this zone, and the organisms that live here must rely on other sources of food, such as nutrients that sink from the upper layers of the lake or organic matter that falls from the surface.
The pelagic zone is the open water of a lake, and it is where most of the photosynthesis takes place. The littoral zone is the shallow water along the edge of a lake, and it is where most of the plants and animals live. The euphotic zone is the upper layer of a lake where there is enough light for photosynthesis to take place.
The profundal zone is important because it provides a home for a variety of organisms, including many that are not found in other parts of the lake. It also plays a role in the cycling of nutrients in the lake.