One is in the U.S.at the Centers for Disease Control, where there is a sample of variola, which is kept, you know, frozen on ice in a heavily guarded facility.

一个在美国的疾病控制中心,那有一支天花病毒的样本,冰冻后置于重重保护之下

耶鲁公开课 - 生物医学工程探索课程节选