The under surface of an arch, is called A. Soffit B. Intrados C. Haunch D. Back

The correct answer is: B. Intrados

The intrados is the undersurface of an arch. It is the curved surface that forms the bottom of the arch. The intrados is typically made of stone, brick, or concrete. It is an important structural element of an arch, as it helps to support the weight of the arch and the structure above it.

The other options are:

• Soffit: The soffit is the underside of any architectural element, such as a beam, lintel, or arch. It is typically made of wood, metal, or plaster.
• Haunch:
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  The haunch is the curved surface of an arch that forms the transition between the intrados and the extrados. It is typically made of the same material as the intrados.
• Back: The back of an arch is the vertical surface that faces away from the viewer. It is typically made of the same material as the intrados.