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“為什么下水道的井蓋都是圓的”，這可是微軟面試的經典怪題。微軟出這道題的目的如何，我們不得而知。不過，我能向您保證一件事，那就是看了下面這篇文章后，您肯定能從科學的角度回答對這個問題。

Manholes, which interconnect underground sewerage pipes, and serve as a point of entry for cleaning the pipes, are located at every major sewer pipe junction, and are capped with round manhole covers. The reason for the circular construction of these covers is, quite simply, that covers of any other shape would fall through the manholes by virtue of their varyingdiameters. Circular manhole covers do not vary in width, or in diameter, as is the case with these other shapes, thus remaining in place despite the street traffic runningroughshodover them.

Manufacturers craft the manhole covers together with the smaller sized lip, upon which they rest, at the same time to ensure a tightly sealed fit. Additionally, the manufacture of circular manhole covers is easier and more accurate than the manufacture of covers of any other shape. Lastly, round manhole covers, once removed, require less lifting and less manpower, as their shape allows them to be rolled.

diameters: 直徑

roughshod: 裝有防滑釘的

（英語點津 Annabel 編輯）