The correct answer is A. Jambs.
Jambs are the vertical sides of a door frame. They are typically made of wood, metal, or plastic, and they are installed on either side of the door opening. Jambs support the door and keep it in place, and they also provide a surface for the door to swing on.
Posts are the vertical supports that hold up the roof of a building. They are typically made of wood, metal, or concrete, and they are installed at regular intervals along the length of the roof. Posts transfer the weight of the roof to the foundation of the building.
Reveals are the exposed edges of a door frame. They are typically the same width as the jambs, and they are located between the jambs and the door. Reveals provide a finished look to the door frame, and they also help to seal the opening between the door and the wall.
Styles are the horizontal members that support the header in a door frame. They are typically made of wood, metal, or plastic, and they are installed at the top of the jambs. Styles transfer the weight of the header to the jambs.