Answer:
D. high-pressure air sinking into
Explanation:
The atmosphere is made up of air, and the air is made up of various gases that exert pressure on the Earth's surface. This pressure, which we call atmospheric pressure, will depend on the altitude of the location. In higher places, such as hills and mountains, we will be far from the surface of the planet, so the air will be thinner, and the pressure will be less. In lower places, such as on the beach, the air layer is larger, and the air pressure is higher. Because of this influence of the altitude of a location on the air pressure, we can conclude that in a type of local wind called valley breeze, if the wind blows the mountain slopes from a valley, this means that there must be air high pressure sinking in the valley.