The correct answer is D. Cell wall.
The cell wall is a rigid structure that surrounds the cell membrane of plant cells. It is made of cellulose, a type of carbohydrate, and provides support and protection for the cell. The cell wall also helps to regulate the movement of water and other substances into and out of the cell.
The cell membrane is a thin, flexible structure that surrounds the cytoplasm of all cells. It is made of lipids and proteins, and its main function is to protect the cell from the environment and to control the movement of substances into and out of the cell.
Chitin is a type of polysaccharide that is found in the exoskeletons of insects and other invertebrates. It is also found in the cell walls of some fungi. Chitin is a strong, rigid material that provides support and protection for the organism.
The epidermis is the outermost layer of cells in plants. It is made of a single layer of cells that are tightly packed together. The epidermis protects the plant from the environment and helps to regulate water loss.
In conclusion, the cell wall is the structure that provides a definite shape to the cell and makes it rigid. The cell membrane, chitin, and epidermis are all important structures, but they do not provide the same level of support and protection as the cell wall.