certain – n. known for sure; unquestioned

quantity – n. the amount of number of things

refer – v. to mean; to direct one's attention to

trend – n. a general direction of change; a way of behaving that is developing and becoming more common

vulnerable – adj. open to attack, harm, or damage

pandemic – n. a disease that has spread across a large area

intensive – adj. involving very great effort or work

couple – adj. meaning two

pattern – n. the regular and repeated way in which something happens or is done