The correct answer is D. Perpendicular to the direction of bedding planes.
Bedding planes are the planes of weakness in a rock mass. They are formed when the rock is deposited in layers and then compacted. The pressure acting on the stones in stone masonry construction should be perpendicular to the direction of bedding planes to prevent the stones from sliding along the planes.
If the pressure is applied along the direction of bedding planes, the stones will be more likely to slide along the planes and the structure will be less stable.
If the pressure is applied at 45° or 60° to the direction of bedding planes, the stones will be more likely to break along the planes and the structure will also be less stable.
Therefore, the pressure acting on the stones in stone masonry construction should be perpendicular to the direction of bedding planes to ensure the stability of the structure.