题目内容
《特种设备安全监察条例》中的压力管道是指最高工作压力大于或等于0.1MPa(表压)的气体、液化气体、蒸汽介质或者可燃、易爆、有毒、有腐蚀性、最高工作温度高于或等于标准沸点的液体介质，且公称直径大于()mm的管道。
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How long has Ms. Johnson worked in her field？
Why are some residents hesitant about the proposals？
A．By grinding heated limestone （石灰石) and clay and mixing them with water.B．By mixin
听力原文： One of the important materials used in the construction of buildings and roads is cement. It is a powder made mainly from limestone and clay. Even though the ancient Egyptians and Romans used a kind of cement, it was not until 1824 that an English bricklayer developed cement strong enough for modern roads and buildings.
While the bricklayer was experimenting in his kitchen, he found that a mixture of limestone and clay that had been heated formed a substance. This substance became hard and stone-like as it cooled. When it was grounded into a fine powder, it could be stored.
When the powder was mixed with water, it made an excellent quality of cement that quickly hardened in sunlight or even under water, it made an excellent quality of cement that is used today.
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