We'll think about it in section, how you don't need to vaccinate everybody, but you just need to vaccinate a critical number in order to stop the disease from progressing through a community.

我们在讨论会上讲这个,为什么不需要给每个人都接种,但你只需要让接种人数达到一个临界值,就能阻止这个疾病在社会中传播

耶鲁公开课 - 生物医学工程探索课程节选

Agricultural villages will have existed all over the place in the late Stone Age, in the Neolithic Period, as it is known. But there is a difference and the critical difference is that a city contains a number of people who do not provide for their own support.

农业村庄在石器时代后期,以及新石器时代随处可见,但二者是有区别的,最重要的区别在于,城市能容纳,相当数量,无需自给自足的人口

耶鲁公开课 - 古希腊历史简介课程节选