VOA慢速英语:美国宇航局准备在火星上进行首次直升机飞行试验

battery – n. a device that is placed inside a machine to supply it with electricity

milestone – n. an important point in the progress or development of something

insulation – n. a material used to stop heat, cold, sound or electricity from escaping or entering

rotor – n. a part of a machine that spins, especially the device supporting the turning blades of a helicopter

microbial – adj. relating to microbes (very small living things)

mission – n. the flight of a spacecraft to perform a task or job