VOA慢速英语:美国公司展示新型超音速试验机

milestone – n. an event that reaches never before seen levels

supersonic - adj. faster than the speed of sound

efficient – n. working well and not wasting time or energy

emission – n. the act of sending gas, heat or light out into the air

carbon-neutral– adj. not producing carbon emissions

propulsion – n. the force produced by a system for moving, or propelling, a vehicle or other object

wind tunnel – n. a closed passage of room through which currents of air are forced in order to study the effects of moving air on aircraft and other vehicles