这是问题：为什么下水道井盖是圆的？

Here's the question: Why are manhole covers round?

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本实用新型是对铁骨架混凝土结构下水道井盖的改进。

The utility model relates to the improvement on a manhole cover with an iron skeleton concrete structure.

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戈福说，目前，黑市上一块重达40公斤的下水道井盖可以卖到大约6欧元。

A 40 kg sewer lid can be sold on the black market for roughly 6 euros (4 pounds), Goffaux said.

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