It's hardly surprising that weather is a favorite topic for so many people around the world—it affects where we choose to live, what we wear, our moods, and perhaps even our national characteristics.Studies have shown that changeable weather can make it difficult to concentrate, cloudy skies slow down reaction, and hot，dry winds make many people badtempered. If you live in a place like Britain, where the weather seems to change daily if not hourly，you could be forgiven for thinking that the weather is random.In fact the weather is controlled by systems which move around areas of the globe.In the UK the weather depends on depressions (低压气流), often called lows，and anticyclones(反气旋)，also known as highs.These systems start in the Atlantic Ocean, and make their way across the British Isles from the west to the east.Highs bring sunny weather, while lows bring rain and wind.In modern times, human activities seem to be altering weather patterns.Gases produced by heavy industry change the temperature of the earth's surface，and affect cloud formation.Some researchers say that factories in Europe and North America may have been one of the causes of the droughts in Africa in the 1980s. The human race has always tried to guess the weather，especially in areas of the world where there are frequent changes.Traditional rhymes point to early attempts to identify weather patterns; popular poems include： Red sky at night, shepherd's delight；red sky in the morning, shepherd's warning. Flies will swarm before a storm. Rain before 7，clear by 11. While folk wisdom can provide a guide to help forecast weather, today's methods of prediction increasingly rely on technology.Satellites, balloons，ships, aircrafts and weather centers with sensitive monitoring equipment, send data to computers.The data is then processed, and the weather is predicted.However，even this system cannot predict weather for longer than about a week. 小题1:When weather keeps changing，________.
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