The external wind pressure acting on a roof depends on

Answer: Option B

The external wind pressure acting on a roof is influenced by several factors related to the geometry and characteristics of the roof surface.

One important factor is the slope of the roof. The angle or pitch of the roof changes the way wind flows over the surface, which affects the magnitude and direction of the pressure acting on it.

Another factor is the degree of permeability of the roof. If the roof allows air to pass through openings or gaps, the airflow pattern and pressure distribution around the roof surface can change.

Therefore, the external wind pressure depends on both the slope of the roof and the permeability characteristics of the roof.

Hence, the correct answer is Option C: Both (A) and (B).