VOA慢速英语:世卫组织称全球新冠肺炎实际感染人数可能远超确诊人数

vast – adj. very big in size or amount

positive – adj. good, hopeful, useful

opportunity – n. a chance; a series of events that make it possible to do something

contact-tracing – n. the process of identifying persons who may have come into contact with an infected individual