题干

用如图所示的装置探究燃烧条件.在铜板上放三根火柴棍,a火柴头上盖一小堆沙子.在a火柴头下方用酒精灯加热.观察到以下现象:a火柴不燃烧,b火柴比c火柴先燃烧.

①a不燃烧的原因是____.

②对比b和c的现象,关于燃烧条件,可以得到的结论是____

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答案(点此获取答案解析)

没有与氧气接触,燃烧时温度要达到着火点

同类题2

材料一:从2014年6月下旬至今,国际油价大幅下跌,11月5日,美国纽约商品交易所原油期货价格下跌至77.19美元/桶,布伦特原油期货价格为82.95美元/桶,欧佩克一揽子原油报收为78.11美元/桶,三价格均较6月最高点跌幅近1/4。造成国际油价持续下跌的原因很多:一是随着非常规油气勘探开发技术的不断进步,水平井、深井、水压裂、地质大数据分析、地下随控技术在常规油气开采中也被大量使用,从而导致石油和天然气产量增加,生产成本不断下降。二是美国推行页岩油气革命,近年,由于页岩气勘探开发相关技术的突破,使美国的页岩气产量快速增长。在美国使用天然气作为动力车船开始快速增加,正在形成不可逆的能结构性转型,使天然气替代石油的压力剧增。三是国际油价下跌的同时,全球石油日供应量却增长了近91万桶,OPEC国家与非OPEC国家都在增产,另外2014年,全球各国经济复苏不如预期,欧盟经济仍深陷欧债危机之后的泥沼之中,中国作为最大的新兴市场国家的经济增速在显著放缓,日本经济刺激政策的效果并不明显,这些因素共同导致了全球市场石油需求变得疲弱。

材料二:“金字招牌”助力旅游“强身健体”。2014年9月,宁德世界地质公园中期评估顺利通过,这一成果势必为我市旅游产业提档升级全面实施品牌战略奠定良好的基础。

同类题5

      Students these days often have a lot of worries. Sometimes they have problems with their schoolwork, and sometimes with their friends.      Some people think the worst thing is to do nothing. Laura Mills, a teenager from Washington, agrees. “Problems and worries are normal in life,” says Laura. “But I think talking to someone helps a lot. If we don't talk to someone, we'll certainly feel worse.”
    Laura once lost her purse, and worried for days. She was afraid to tell her parents shout it. She even walked three miles to school each day because she didn't have any money. She just kept thinking. “If I tell my parents, they'll be angry!” But in the end, she talked to her parents and they were really understanding. Her dad said he sometimes made careless mistakes himself. They got her a new purse and asked her to be more careful. “I will always remember to share my problems in the future!” Laura says.
       Robert Hunt advises students about common problems. He feels the same way as Laura. “It is best not to avoid our problems. We should always try to solve (解决) them.” He thinks that you can first find someone to talk to. This person doesn't need to be an expert (专家) like himself. Students often forget that their parents have more experience than them, and are always there to help them.
    In English, we say that sharing a problem is like cutting it in half. So you're halfway to solving a problem if you talk to someone about it!