But in the 13th century, the capital city,Angkor,died off, and a new scientific study indicates that climate, specifically decades of drought interspersed with intense monsoons, helped bring down the Khmer capital.

VOA: standard.2010.04.05

In 13th century India, they knew how to isolate metallic zinc.

在13世纪的印度，我们知道了如何提取金属锌。

麻省理工公开课 - 固态化学导论课程节选

In 13th century India, they knew how to isolate metallic zinc.

在13世纪的印度，我们知道了如何提取金属锌。

麻省理工公开课 - 固态化学导论课程节选