I'd never thought about how that s got there, but now I see that that genitive s is just a grammatical sibling of the possessive 's in Mary's house.

我自己则从未想过词尾上怎么会带上了这个s，不过现在我知道了这个属格的s跟玛丽的房子(Marys house)里的所有格的s在语法上都是亲兄弟。

youdao

We shouted loudly at the highest point of U. s... I thought there might come a white-haired old man anytime who would calm us down in the eastern prairie during the whole night.

我们在美国的最高处大声叫喊，我想整个夜晚，在东部平原，随时可能有一个白发老人向我们走来，让我们安静。

youdao

We shouted loudly at the highest point of U. s... I thought there might come a white-haired old man anytime who would calm us down in the eastern prairie during the whole night.

我们在美国的最高处大声叫喊，我想整个夜晚，在东部平原，随时可能有一个白发老人向我们走来，让我们安静。

youdao