چندگزینه‌ای، پایان جمله و سؤال کوتاه‌پاسخ

A For centuries, people living in the hot, dry regions of Iran and around the Persian Gulf kept their homes cool without any electricity at all. Their main tool was the windcatcher, or badgir: a tall tower on the roof with openings near the top that catch passing breezes and send them down into the rooms below. In the old city of Yazd, hundreds of these towers still rise above the rooftops, and some are more than twenty metres high. B The principle is simpler than it looks. Wind blowing against the tower is pushed downwards through channels inside it, while warm air in the house escapes through openings on the side facing away from the wind. Even on still days, the tower can work like a chimney: as the sun heats the air inside it, this air rises and leaves at the top, drawing cooler air in from shaded courtyards. In some designs, the incoming air first passes over an underground water channel, known as a qanat, which can lower its temperature by several degrees. C Windcatchers fell out of use in the twentieth century, when electric air conditioning became widely available. Many owners blocked their towers to keep out dust and insects, and new buildings were designed without them. Recently, however, architects have begun to look at them again. Air conditioners now account for a large share of summer electricity demand in hot countries, and power cuts during heatwaves have shown how dependent cities have become on them. D Modern versions do not simply copy the old towers. Researchers have tested designs that use sensors and small fans to control the airflow, and some add damp pads to cool the air further. Early tests suggest that such systems can noticeably reduce the energy needed for cooling, although results in real buildings have so far been more modest than computer models predicted. E Critics point out that windcatchers are not suitable everywhere. In humid climates, cooling the air with water makes rooms uncomfortable, and in crowded city centres, tall neighbouring buildings may block the wind before it reaches the tower. Supporters accept these limits, but they argue that, combined with thick walls, shading and careful planning, the idea could help keep cities liveable as summers grow hotter.