The wave of COVID-19 infections prompted New York Mayor Bill de Blasio today to close the nation's largest public school system again.

COVID-19感染的浪潮促使纽约市长比尔·德布拉西奥今天再次关闭美国最大的公立学校系统。

The second law of thermodynamics states that closed systems tend towards disorder: you won't see a shattered glass return to its pristine state.

热力学第二定律指出，封闭系统倾向于无序：你不会看到一个破碎的玻璃恢复到原始状态。

Officials say they decided to close down the entire public school system out of what they called an abundance of caution after they've received a threat in an email.

官方决定关闭所有公立学校，并称收到威胁邮件，安全隐患堪忧。