黑死病，为什么夺走几千万人？

Long ago, a terrible plague hit Europe. 很久以前，欧洲爆发了可怕的瘟疫。 People called it the Black Death. 人们叫它黑死病。 It spread fast through the crowded towns. 它在拥挤的城镇里飞快传开。 Every three people, one was taken away. 每三个人里，就有一个被带走。 Tens of millions of lives were lost. 几千万人失去了生命。 It was one of the worst disasters in history. 这是历史上最惨的灾难之一。