The correct answer is: A. 10% of wall area.
The area of openings for buildings of large permeability is more than 10% of wall area. This is because buildings with large permeability need to have a lot of openings in order to allow for ventilation and natural light. If the area of openings is too small, the building will not be able to ventilate properly and this could lead to health problems for the occupants.
Option B is incorrect because 20% of wall area is not enough to allow for proper ventilation. Option C is incorrect because 30% of wall area is still not enough to allow for proper ventilation. Option D is incorrect because 50% of wall area is too much and could lead to energy loss.
In conclusion, the area of openings for buildings of large permeability is more than 10% of wall area. This is because buildings with large permeability need to have a lot of openings in order to allow for ventilation and natural light.