The correct answer is A. retaining wall.
A retaining wall is a structure that is used to hold back soil or other materials from sliding down a slope. They are often used in construction projects, such as when building a road or a house on a hillside. Retaining walls can be made of a variety of materials, including concrete, stone, and brick.
A breast wall is a type of retaining wall that is built against a slope to prevent the soil from sliding down. It is typically shorter than a retaining wall and is not as heavily loaded. Breast walls are often used in landscaping projects to create terraces or to support retaining walls.
A parapet wall is a low wall that is built along the edge of a roof or other elevated surface to prevent people or objects from falling off. Parapet walls are typically made of concrete or stone and are often topped with a railing.
None of the above is not the correct answer.