The correct answer is D. All the above.
Atmosphere pressure, air density, and reduced level are all meteorological conditions that influence the size and location of an airport.
Atmosphere pressure is the force exerted by the weight of the air above a given point. It is measured in millibars (mb). The higher the atmosphere pressure, the denser the air and the easier it is for aircraft to take off and land.
Air density is the mass of air per unit volume. It is measured in kilograms per cubic meter (kg/m3). The higher the air density, the more lift an aircraft can generate.
Reduced level is the altitude at which the atmospheric pressure is equal to 1013.25 mb. It is used to calculate aircraft performance.
The size and location of an airport are also influenced by other factors, such as the availability of land, the proximity of population centers, and the cost of construction.