在一般情况下，单位时间内高温物体向低温物体传递的热量与两个物体的温差成正比．冬天的北方比较寒冷，房间内都有供暖系统．如果房外温度为﹣20℃，则房内温度为18℃；如果房外温度为﹣30℃，则房内温度为12℃．那么，房间暖气管的温度为（　　）

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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.