Weather variation of vacuum value

A rise in mercury indicates an increase in air pressure.

There are three factors that affect air pressure: altitude, humidity and temperature.

The higher the altitude, the thinner the air and the lower the air pressure.

The higher the humidity, the lower the air pressure, and the weather is obviously sultry before and after the rain.

The higher the temperature, the lower the air pressure, which means that the air density is high and the air pressure is high when it is cold.

So the answer should be: D.

When the weather turns from cloudy to sunny, the humidity in the air decreases, the air density increases and the air pressure increases.