儿童、青少年以及伤病员要多吃一些奶、蛋、鱼、肉，是因为人的生长发育和受损细胞的恢复和更新，都离不开（    ）

甲、乙、丙和丁四个图分别表示有关量的变化规律，下列描述中，正确的是（　　）

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通过小学科学课程和初中物理的学习知道，磁体能够吸引铁、钴、镍等铁磁性物质，不能吸引铜、铝等金属．小明看到一个铜管与磁铁相互作用的有趣实验：如图所示，实验中把一个钕磁铁（强力磁铁）通过铜管时，磁铁下落是缓慢的；越强的磁铁和厚的铜管，磁铁下降越慢．小明分析产生这种现象的原因可能是：钕磁铁下降时，在铜管中产生了 ____，随即使铜管周围存在 ____，与钕磁铁产生相互作用，使磁铁下降减慢

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    Is there link between humans and climate change or not? This question was first studied in the early 1900s. Since then, many scientists have thought that our actions do make a difference. In 1997, the Kyoto Protocol explained our role in the Earth's changing atmosphere and set international limits for gas emissions(排放) from 2008 to 2012. Some countries have decided to continue these reductions until 2020. More recently, the Paris Agreement, stuck by nearly 200 countries, also aims to limit global warming. But just now how much warmer it will get depends on how deeply countries cut carbon emissions.