Modern life makes us tired, right? But research from societies in Africa and South America suggests people in the ancient world slept only 6.5 hours a night.

Modern life makes us tired, right? But research from societies in Africa and South America suggests people in the ancient ...

这次致命事故提出了一个严重问题：在美国首都上空为何会发生相撞事故？专家认为这两架飞机出现在同一空域有些匪夷所思 ...