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  3. Now satellites are helping to forecast the weather. They are in space, and they can reach any part of the world. The satellites

Now satellites are helping to forecast the weather. They are in space, and they can reach any part of the world. The satellites

admin2011-07-17  52
问题 Now satellites are helping to forecast the weather. They are in space, and they can reach any part of the world. The satellites take pictures of the atmosphere (大气), because this is where the weather form. They send these pictures to the weather stations. So meteorologists(气象学家) can see the weather of any part of the world. From the pictures, the scientists can often say how the weather will change.
   Today, nearly five hundred weather stations in sixty countries receive satellite pictures. When they receive new pictures, the meteorologists compare them with earlier ones. Perhaps they may find that the clouds have changed during the last few hours. This may mean that the weather on the ground may soon change, too. In their next weather forecast, the meteorologists can say this.
   So the weather satellites are a great help to the meteorologists. Before satellites were invented, the scientists could forecast the weather for about 24 or 48 hours. Now they can make good forecasts for three or five days. Soon, perhaps, they may be able to forecast the weather for a week or more ahead.
Meteorologists forecast the weather ______ .
选项 A、when they have received satellite pictures
B、after they have compared new satellite pictures with earlier ones
C、before they received satellite pictures
D、during they study satellite pictures
答案B
解析 根据第二段的说明我们知道，气象学家通过拍摄的新的照片和之前拍摄的照片比较，发现天气可能发生的变化。A项指当他们接收到卫星图片的时候，这时候还没有比较，所以没办法预报天气。B项指在他们将新的图片和之前的比较之后，这个符合文章的意思。C项指在他们接收到卫星图片之前，接收图片之前怎么可能预报天气呢，所以C也不正确。D项指当他们在研究卫星图片的时候，和文章的说明不符。所以答案选B。
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