The answer is D. Beam.
A house is a building that is used for habitation. It is typically made of wood, brick, or concrete, and has a roof to protect it from the elements. Walls are the vertical surfaces that enclose a house, and they are typically made of the same materials as the house itself. A roof is the covering that protects a house from the rain and snow, and it is typically made of shingles, tiles, or metal. A beam is a long, horizontal piece of wood or metal that is used to support a structure, such as a roof or floor.
In this question, all of the options except for beam are parts of a house. A house has walls, a roof, and a floor. A beam is not a part of a house, but it is a structural element that can be used to support a house.