Wouldn’t it be great if you could just look up at the sky and read the weather forecast right away? Well, you can. The forecast

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问题     Wouldn’t it be great if you could just look up at the sky and read the weather forecast right away? Well, you can. The forecast is written in clouds. If you can read that writing, you can tell something about the atmosphere. With some practice, you can become a pretty good weather forecaster. Who knows, you might even do as well as meteorologists.
    Meteorologists use much more information than just the appearance of the clouds to make their forecast. They collect data from all over the world. Then they put it into powerful, high-speed computers. This does give the meteorologists an advantage, because they can track weather patterns as they move from west to east across the country. But you have an advantage, too. You can look at the sky and get your data directly. A meteorologist uses a computer forecast that’s several hours old to make a local forecast.
    What are you seeing when you look at a cloud? "A picture of moisture is doing in the atmosphere," says meteorologist Peter Leavitt. There’s moisture throughout the atmosphere. Most of the time you don’t see it, because it’s in the form of an invisible gas called water vapor. Sometimes, the temperature of the air gets cold enough to cause the water vapor to change to liquid water. It’s called condensation, and we see it happen all the time(for example, when humid air from the shower hits the cold glasses of a mirror). When enough water vapor condenses, droplets come in the air. These droplets scatter light. A cloud is seen.
    Watching clouds over a day or two tells you a lot more than a single cloud about the weather to come. Changes in clouds show changes in the atmosphere. You should begin to notice patterns. Certain clouds, following each other in order, can signal an approaching storm. But don’ t take our word for it; see for yourself.
Meteorologists make their weather forecast by______.

选项 A、watching clouds constantly
B、collecting data from parts of the world
C、calculating analyzing datas
D、watching the sky

答案C

解析 细节题。根据文章第二段可知,科学家做天气预报更多的是使用来自世界各地的数据,并通过更强大的、高速运行的计算机来分析,故C符合文意,为此题答案。
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