When astronauts return from space walks and remove their helmets， they are welcomed back with a specific smell， which is distinct and weird： something like seared steak， also like hot metal or welding smoke.
　　Three-time spacewalker Thomas Jones has said， “Space carries a distinct odor of ozone. It is acrid and smells a little like gunpowder.”
　　But how does it smell weird？ It turns out that it is the atmosphere that gives space the special odor. According to a research， when astronauts move their bodies from space to the station， they bring some particles back inside. The odor they smell comes from the high-energy vibrations in these particles which mix with the air.
　　“Each time， when I pressed the airlock， opened the hatch and welcomed two tired workers inside， a peculiar smell tickled my nose，” astronaut Don Pettit recalled.“At first I thought it must have come from the air channel. Then I noticed that this odor was on their suits， helmets， gloves， and tools. It was more obvious on cloths than on metal or plastic surfaces.”
　　So NASA， now， is trying to reproduce that odor for training purposes—to help astronauts adapt better to the odor of the extra-atmospheric environment.
　　helmet头盔
　　distinct 明显的
　　weird 奇怪的
　　sear 烤焦
　　steak 牛排
　　welding 焊接的
　　odor气味
　　ozone 臭氧
　　acrid 刺鼻的
　　gunpowder火药
　　particle粒子
　　vibration振动
　　hatch舱门
　　tickle （使）发痒
　　extra？鄄atmospheric大气层外的
　　Where does the weird smell of space come from？
　　A. The vibration in particles which mix with the air.
　　B. The suits， helmets， goloves which astronauts wear.
　　C. The air channel of the space station.
　　（Find the Key in this issue）