美国各州为全国最大规模的疫苗接种做准备

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dose –n. the amount of a medicine, drug or vitamin that needs to be taken at one time

immunization –n. to give a person a vaccine to prevent infection that causes a disease

track –v. to follow and watch the progress of a process or project

minus –adj. having a value that is below zero, of example, of a temperature

challenge –n. a difficult task or problem to be solved

convince –v. to persuade someone to do something