Hxen.com's tips：Every day persisted can learn English well!-->■Learn English Everyday■
alarming – adj. something that is worrisome or dangerous
routine – adj. a common or usual activity
immunity – n. to be vaccinated against a disease
pandemic – n. a contagious disease that moves from one country to another
immunize – v. to vaccinate someone against a disease
challenge - n. something that is difficult to do
