Hxen.com's tips：Every day persisted can learn English well!-->■Learn English Everyday■
mask – n. a covering used to protect your face or cover your mouth
underlying – adj. used to identify the idea, cause, problem, etc., that forms the basis of something
transmission – n. the act or process by which something is spread or passed from one person or thing to another
teenager – n. a person between 13 and 19 years old
solely – adv. only or just
