ruins作主语 谓语单复数

老师请看 http://www.chinadaily.com.cn/a/201907/09/WS5d244a82a3105895c2e7c86c.html 里的两句话：

The archaeological ruins of Liangzhu in Hangzhou, Zhejiang province, which date back 5,300 years, were inscribed onto the UNESCO World Heritage list on July 9, 2019, during the 43rd session of the World Heritage Committee in Baku, Azerbaijan.

The ruins, whose core area covers 14.3 square kilometers in the northwest of Hangzhou, is considered an important representation of early urban civilization, with rice-cultivating agriculture as the economic foundation.

请问第二句谓语动词用单数的理由。能否再举个相似的例子。