Hxen.com's tips：Every day persisted can learn English well!-->■Learn English Everyday■
smog - n. fog mixed with smoke : a cloud of dirty air from cars, factories, etc., that is usually found in cities
microscopic - adj. able to be seen only through a microscope; extremely small
mask - n. a covering used to protect your face or cover your mouth
ton - n. a unit for measuring weight that equals 2,000 pounds (907 kilograms)
monitor - v. to watch, observe, listen to, or check (something) for a special purpose over a period of time
stability - n. the quality or state of being stable
power plant - n. a building or group of buildings where electricity for a large area is produced
