18．
Scott Kelly，an American astronaut，returned to earth on March 2，2016．He was taller by nearly 1.5inches （3.81cm）when he landed on Earth after his 340-day space mission on the International Space Station （ISS）．
His change in height，which lasted about two days，raised the question：What are the effects of a long-term stay in space？
As you probably know，there is no gravity in space．This not only causes difficulties in everyday actions like eating，walking and sleeping，but also problems for the human body．
The first problem is the air．Without gravity，carbon dioxide cannot spread during breathing，but gathers around the body and causes headaches．More than that，human feelings of movement are affected，which could make people feel sick．
The body's fluids（液体）don't work well in weightlessness，making blood flow upward instead of down to the lower legs，and astronauts'faces become fatter than normal．Gaps between bones also become larger because humans cannot stand up straight．The spine（脊柱）can also get bigger in zero gravity．
In addition，human bodies become weaker because of the lack of gravity and space to move around in．Some astronauts said that after they returned，their muscles hurt and their skin became very sensitive（敏感的）Kelly said during his first press conference，"It was almost like my body was on fire wherever I sat or lay or walked．"
However，the research into the effects of long-term space flight on human bodies and minds never stops．There are many actions that astronauts can take in space．They can take vitamin D for bone growth，wear special belts on their legs to keep blood in their lower bodies and do strength coaches'exercises．The fans in the ISS also help spread carbon dioxide around．"We will do further research．"NASA Administrator Charles Bolden said，"I believe it will be meaningful to human-being．"
88．Something occured to Kelly's body when he finished his space mission，didn't it？Yes，it did
89．People mayhave a headache，if carbon dioxide cannot spread during breathing．
90．What will happen to astronauts'faces in space？They become fatter．
91．Why did Kelly feel burned when he was sleeping according to the text？After they returned，their muscles hurt and their skin became very sensitive．
92．What can astronauts do to keep fit in space？They can take vitamin D for bone growth，wear special belts on their legs to keep blood in their lower bodies and do strength coaches'exercises．
93．Do you agree that the research is meaningful to human-being？Why？Yes，I think it is helpfulto the astronauts．．
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