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  3. 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

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

admin2015-02-09  32
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 can make their weather forecast______.
选项 A、by using information of the appearance of the clouds only
B、by collecting data from parts of the world
C、by calculating and analyzing this data
D、by watching the sky
答案C
解析
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