A、It’s the ultimate cause of winds. B、It causes vertical movements of air. C、It reduces differences in air pressure. D、It’s used

We only have a few minutes left so I’d like to go over a couple of points before we move on.
    Remember, although there are both horizontal and vertical movements of air, the term "wind" is applied only to horizontal movements, and more air is involved in horizontal movements than those vertical movements. And what causes these horizontal movements? Ultimately, it’s the solar radiation, because the unequal heating of the earth rather than the atmosphere produces horizontal differences in air pressure. These differences set winds in motion. Essentially, winds are the nature’s way of balancing uneven distribution of air pressure over the earth. Secondly, let me repeat my answer to the question we had before about wind direction. Many people get confused by what they hear in weather forecast.
    We talk about wind direction in terms of where the wind’s coming from, not where it’s blowing to. There is a good reason to this. To weather broadcasters, the origin of winds is more important than its destination. The winds’ origin helps them predict the weather.
    Logically, in the northern hemisphere, a north wind tends to bring cold weather, and the south wind warm weather. I haven’t forgotten vertical movements of air. We don’t have time today to talk about them in depth. In our next class then, I’ll begin by discussing updraft and downdraft and how they affect the weather.
    I suspect most of you can guess which of the two brings warm weather, and which brings cold.