VOA慢速英语:Do Face Masks Protect Against Air Pollution?

premature – adj. happening, arriving, existing, or performed before the proper, usual, or intended time;

exposure – n. the fact or condition of being affected by something or experiencing something

inexpensive – adj. reasonable in price

gold standard – adj. a model of excellence

rate – v. to determine or assign the relative rank or class of

substitute – v. to put or use in the place of another

attainable – adj. to be able to come into possession of

exhalation – n. the action of forcing air out of the lungs

valve – n. a mechanical device that controls the flow of liquid, gas, etc., by opening and closing

snugly– adv. to cause to fit closely

magnitude – n. great size or extent