在线作业：
　　High Dive
　　Cheryl Stems aims to go boldly where no human has ever gone before in a balloon：40 kilometers up into the atmosphere．__1 __．No one has ever leapt from such a height or gone supersonic without an airplane or a spacecraft．Yet Stems，an airline pilot，is not the only person who wants to be the first to accomplish those feats．Two other brave people，an Australian man and a Frenchman，are also planning to make similar leaps．
　　__2__．First，she’ll climb into a cabin hanging from a balloon the size of a football field．Then the balloon will take her high into the stratosphere—the layer of Earth’s atmosphere 12 to 50 kilometers above the planet．“The ascent will take two and a half to three hours．” said Stems．”I’ll be wearing a fully pressurized，temperature-controlled space suit．’’
　　At 40 kilometers。Stems will be able to see the gentle curve of Earth and the blackness of space over head．Then she’ll unclip herself from the cabin and dive headfirst，like a bullet，into the atmosphere. __3__.
　　For high dive，astronaut escape suits are a key to success．Current pilot and astronaut escape suits are guaranteed only a maximum altitude of 21 kilometers．Del Rosso，a NASA engineer of spacesuits and life—support systems，said the suit designed for Stern’s jump could serve as a model for the lethal environment of higher climbs．__4__.The first hazard is oxygen-deficient air．Any person without an additional oxygen supply at 40 kilometers would die within three to five seconds．The second hazard is low atmospheric pressure．Atmospheric pressure is much lower at high altitudes than it is at sea level．The low atmospheric pressure of the upper stratosphere causes the gases in body fluids to fizz out of solution like soda bubbles．__5___．Other hazards include temperatures as low as-55 degrees Celsius，flying debris，and solar radiation．
　　For Sterns to survive，her spacesuit will have to protect her from all of these hazards．“A spacesuit is like a one-person spaceship。”Del Rosso explained．“You have to take everything you need in a package that’s light enough，mobile enough，and tough enough to do the job．You Can’t exist without it．”

　　A．  It will handle several major hazards．
　　B．  Escape suits are tough enough to stand the atmospheric pressure of the upper stratosphere
　　C．  From there，she’11 take a death-defying leap back to Earth at supersonic speed．
　　D．  “In 30 seconds，I'll be going Mach(马赫)speed，”said Stems．
　　E．  How will Stems make her giant jump?
　　F    In short，blood boils．

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