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  3. The planets seemed like pretty small places. At the same time, Earth seemed a lot larger than it does now. No one had ever seen

The planets seemed like pretty small places. At the same time, Earth seemed a lot larger than it does now. No one had ever seen

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问题    The planets seemed like pretty small places. At the same time, Earth seemed a lot larger than it does now. No one had ever seen our planet as a planet: a blue marble on black velvet, coated with water and air. No one knew that the moon was born in an impact. No one fully appreciated that humanity was becoming a geologic force in its own right, capable of changing the environment on a global scale. Whatever else the Space Age has done, it has enriched our view of the natural world and given us a perspective.
   National Research Council(NRC)panels periodically ask whether the world’ s planetary exploration programs are on track. The list of goals that follows synthesizes their priorities.
   1. Monitor Earth’ s Climate
   The venerable Landsat series, which has monitored the surface since 1972, has been on the fritz for years, and the U. S. has Department of Agriculture has already had to buy data from Indian satellites to monitor crop productivity. For some types of data, no other nation can fill in.
   2. Prepare an Asteroid Defense
   Like climate monitoring, guarding the planet from asteroids always seems to fall between the cracks. Neither NASA nor the European Space Agency(ESA)has a mandate to stave off human extinction. It would take 15 years or longer to mount a defense against an incoming body, assuming that the technology were ready to go.
   3. Seek Out New Life
   Before Spotnik, scientists thought the solar system might be a veritable Garden of Eden. Earth’s sister worlds proved to be hellish, even when the Mariner probes revealed a cratered moonscape and the Viking landers failed to find even a single organic molecule. But lately the plausible venues for life have multiplied.
   4. Explain the Genesis of the Planets
   Studies of the origin of the planets overlap quite a bit with studies of the origins of life. Jakosky puts it thus: "Venus sits at the inner edge of the habitable zone. Mars sits at the outer edge. Earth sits in the middle. And understanding the differences between those planets is central to asking about life beyond our solar system."
   5. Break Out of the Solar System
   A solar sail 200 meters across could carry a 500-kilogram spacecraft. After launch from Earth, it would first swoop toward the sun, going as it dared—just inside Mercury’s orbit—to get flung out by the intense sunlight.
   "Such a mission, be it ESA-or NASA-led, is the next logical step in our exploration of space, " Wim mer-Schweingruber says. "After all, there is more to space than exploring our very, very local neighborhood." The estimated price tag is about $2 billion including three decades’ operating expenses.
   [A]Like the origin of life, the origin of the planets was a complex, multistage process. Jupiter was the first-born. Did it build up slowly, like the other planets? Did it form farther from the sun and move inward?
   [B]Like a windsurfer, the spacecraft would steer by leaning to one side or the other. Just before pass ing Jupiter’s orbit, it would cast off the sail and glide outward. To get ready, engineers need to design a sufficiently lightweight sail and test it on first.
   [C]So NRC prepares to take some action plans. Extend asteroid search to smaller bodies, perhaps using a dedicated infrared space telescope. Deflect an asteroid in a controlled way as a trial run. Develop an official system for evaluating potential threats.
   [D]The NRC panel called for restoring the lost funding, which pay for 17 new missions over the coming decade, such as ones to keep tabs on ice sheets and carbon dioxide levels—essential for predicting climate change and its effects. People sometimes take the mundane yet urgent task of looking after our own planet for granted.
   [E]Mars is looking hopeful again. Outer-planet moons, notably Europa and Enceladus, appear to have vast underground seas and plenty of life’ s raw materials. Even Venus might have been covered in oceans once. The research is not just about finding companionship in the cosmos. It is about divining our own origins.
   [F]This past spring ESA completed a set of feasibility studies—and promptly shelved them for lack of money. It would take a joint effort with NASA or the Japan Aerospace Exploration Agency(JAXA), or both, to make the plan happen.
选项
答案A
解析 本段的主题是Explain the Genesis of the Planets(解释行星的起源)。作者首先谈到了宜居带和人类起源的问题。由于小标题是关于行星起源的，那么接下来的内容肯定与行星起源有关。A项涉及这方面的内容，以木星为例描述了人类对于木星起源的困惑。而且Like the origin of life，the origin of the planets was a complex，multistage process与前文Studies of the origin of the planets overlap quite a bit with studies of the origins of life观点相似，进一步验证了A项为本题的正确答案。
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