The correct answer is: A. Zero.
The internal wind pressure acting normal to the wall and roof surfaces of a building having a low permeability is taken as zero. This is because the low permeability of the building means that there is little or no air movement inside the building, and therefore no wind pressure.
Option B is incorrect because it suggests that the internal wind pressure is equal to ±0.2p. This is not the case, as the internal wind pressure is always zero for buildings with low permeability.
Option C is incorrect because it suggests that the internal wind pressure is equal to ±0.5p. This is not the case, as the internal wind pressure is always zero for buildings with low permeability.
Option D is incorrect because it suggests that the internal wind pressure is equal to ±0.7p. This is not the case, as the internal wind pressure is always zero for buildings with low permeability.