VOA慢速英语:关于学校重新开课的争论让美国社会产生分歧

challenge – n. a difficult task or problem : something that is hard to do

mask – n. a covering for your face or for part of your face

contact tracing – n. the process of identifying people who may have come into contact with an infected person

board – n. a group of people who manage or direct a company or organization