The Hammurabi Code is the oldest known legal document in human history。（)
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什么叫自生风？自生风的正负号如何决定？在水平烟道有没有自生风？
The Minoan civilization is often regarded as the first advanced civilization of Europe。（)
The Late Middle Ages are often described as a period of crisis and decline。（)
为什么氢离子交换软化设备要防腐？为什么铵离子交换软化设备不要防腐？为什么混合式氢钠离子交换软化水中残留碱度最大？
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