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第1段
1 .<-NARRATOR:->Now listen to part of a lecture on the topic you just read about.
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第2段
1 .<-FEMALE PROFESSOR:->A trip to Mars will definitely be challenging, but scientists have proposed solutions to the problems the reading selection discusses.
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2 .First of all, food, water, and oxygen. Well, astronauts can use hydroponics.
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第3段
1 .Hydroponics is a technique for growing plants with their roots in water rather than in soil.
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2 .It requires relatively little space.
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3 .Using hydroponics, the astronauts should be able to cultivate food crops in the spacecraft.
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4 .In addition, the hydroponically grown plants will recycle wastewater and release it as clean water vapor, which can be collected as drinking water.
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5 .And of course, all plants absorb carbon dioxide and release oxygen, so thanks to hydroponics, the astronauts will also have fresh air to breathe.
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第4段
1 .Second, the effects of zero gravity.
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2 .Over the last few decades, we have launched several space stations orbiting the Earth, and a number of astronauts have spent many months on them in a zero-gravity environment.
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3 .These astronauts have learned to use several techniques to safely manage the effects of zero gravity.
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4 .For example, regular exercise prevents the decrease in muscle mass.
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5 .Likewise, taking vitamins and minerals like calcium slows down the decrease in the astronauts’ bone density.
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第5段
1 .Third, solar radiation. Astronauts traveling to Mars will be exposed to some solar radiation, but this radiation will not be at dangerous levels all the time.
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2 .The Sun only releases dangerous amounts of radiation occasionally, during periods when it's particularly active.
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3 .In order to avoid this threat, the spacecraft could be equipped with special instruments that monitor solar radiation, and with a small shelter that is shielded against radiation but doesn't add much weight to the ship.
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4 .Most of the time, the astronauts would go about their normal business in unshielded areas of the spacecraft.
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5 .But when their instruments detect increased radiation, they could stay in the small shielded area until the danger has passed.
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