7．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 （气象学家）．
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 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 have your brains．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 what moisture （水气） is doing in the atmosphere，"says meteorologist Peter Leavit．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．That's called condensation，and we see it happen all the time，for example，when humid air from the shower hits the cold glass of a mirror．When enough water vapor condenses，droplets form 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，fol1owing each other in order，can signal an approaching storm．But don't take our word for it； see for yourself．
53．According to the passage，ordinary people can tell the weather becauseD．
A．they can look up at the sky
B．they can read weather writings
C．information is stored in computers
D．clouds signal the weather to come
54．Your advantage in weather forecast is thatC．
A．you can keep weather patterns in mind．
B．you have more powerful computers at home
C．your brain works as well as a high-speed computer
D．meteorologists give their data to you as soon as they get them
55．A cloud is formed whenA．
A．there are droplets in the air
B．light is scattered
C．moisture exists in the form of invisible gas
D．water vapor changes to liquid water
56．This passage mainly tells us about howD．
A．to become a weather forecaster
B．to collect data directly
C．to be an assistant to a meteorologist
D．to keep an eye on the weather．
分析 本文是科技说明文，说明普通人可以通过观察云层预测天气．气象学家通过收集世界各地的数据，然后输入强大的高速的电脑，这是气象学家的优势；作为普通人也有优势：有大脑，可以观察云层实时获得数据．那么观察云层能看到什么？（可以看到）关于大气层此时湿度的图片．整个大气层都充满水汽．大部分时间你看不到它，因为它是以一种叫做水蒸气的无形气体的形式存在的．有时，空气的温度下降得足够低，能使水蒸气变成固态的水．这一过程叫凝结．我们一直都能看到凝结的发生（比如，淋浴时湿气碰到冷的镜子而凝结）．当足够的水蒸气凝结之后，小水滴就在空气中形成了．这些水滴能散射光．我们就可以看见云朵了．
观察云层在一、两天内的变化，比单看一块云朵能告诉你更多关于未来天气的信息．云层的变化显示出大气层的变化．你应该从留意天气变化的模型开始．有时，云彩按一定顺序变化，能暗示一场即将到来的暴风雨．但是别相信我们的话；自己去观察吧
解答 53．D．细节理解题．根据文章最后倒数第二句"Certain clouds，fol1owing each other in order，can signal an approaching storm．（一些云按一定顺序变化，能暗示一场即将到来的暴风雨）"可以判断云朵能够预示即将出现的天气，故答案选择D．
54．C．细节理解题．根据第5段中的"But you have an advantage，too．You have your brains．（你也有你的优势，你有你的大脑）"推断普通人的优势是大脑
，气象学家的优势是强大快速的电脑；故推断大脑能够像电脑一样运行，所以答案选择C．
55．A．细节理解题．根据倒数第三段中的"These droplets scatter light．A cloud is seen（这些水滴散光，云出现了）．"判断空气中有了这些水滴就形成云，故答案选择A．
56．D．主旨大意题．本文的开头通过反问句告诉了我们通过抬头看天空的云来预测天气．全文最后一段中"You should begin to notice patterns．Certain clouds，fol1owing each other in order，can signal an approaching storm．（关注一些云的变化模式；有时，云彩按一定顺序变化，能暗示一场即将到来的暴风雨）"又再次重申了作者的主要观点--自己观察云，关注天气．
点评 本文是一篇科技说明文．作者通过解释云的形成告知读者可以通过云来读懂天气．题目中涉及几条细节题，细节题一定要在文章中定位细节，仔细理解细节的内容再做出合理的解答；本题中还涉及一道推断题．推断题要根据文章的主旨和细节合理推断，不能用常识或自己的观点代替推测．
