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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An Egyptian.
B. A Roman.
C. A British.
D. A man named Blake.