《人民日报》评论部主任卢新宁在北大中文系毕业典礼上的致辞中说道：“请记得：你所站立的地方，就是你的中国；你怎么样，中国便怎么样；你是什么，中国便是什么；你如光明，中国便不再黑暗。”这启示我们青少年为实现中国梦应该（   ）
①自觉承担责任履行义务              ②声张正义，主要精力用于揭露社会矛盾问题
③克服冷漠情绪和看客心理          ④明辨是非，自觉抵制某些不良社会风气的诱惑 

一定质量的木炭在氧气和氮气的混合气体的密闭容器中燃烧产生CO和CO₂，且反应后测得混合气体中碳元素的质量分数为24%，则其中氮气的质量分数不可能为（　　）

有学者认为：“从美洲传到东半球的粮食作物、经济作物和水果品种则更多，有玉米、马铃薯、花生、番茄、辣椒、棉花、烟草、可可豆、菠萝、木瓜等等。”这种现象的出现主要是因为（    ）

根据短文理解，选择正确答案。

    People who have lost the ability to understand or use words due to brain damage are called aphasics（失语症患者）.Such patients can be extremely good at something else.From the changing expressions on speakers' faces and the tones of their voices,they can tell lies from truths.

    Doctors studying the human brain have given a number of examples of this amazing power of aphasics.Some have even compared this power to that of a dog with an ability to find out the drugs hidden in the baggage.

    Recently,scientists carried out tests to see if all that was said about aphasics was true.They studied a mixed group of people.Some were normal;others were aphasics.It was proved that the aphasics were far ahead of the normal people in recognizing false speeches—in most cases,the normal people were fooled by words,but the aphasics were not.

    Some years ago,Dr.Oliver Sacks wrote in his book about his experiences with aphasics.He mentioned a particular case in a hospital.Some aphasics were watching the president giving a speech on TV.Since the president had been an actor earlier,making a good speech was no problem for him.He was trying to put his feelings into every word of his speech.

    But his way of speaking had the opposite effect on the patients.They didn't seem to believe him.Instead,they burst into laughter.The aphasics knew that the president did not mean a word of what he was saying.He was lying!

    Many doctors see aphasics as people who are not completely normal because they lack the ability to understand words.However,according to Dr.Sacks,they are more gifted than normal people.Normal people may get carried away by words.Aphasics seem to understand human expressions better,though they cannot understand words.

    李清照现存的词曲中，有四分之一出现了与香炉，焚香相关的意象。为何李清照对香炉会如此情有独钟呢？这要从香炉的用途说起了。

    专门为焚香而设计的香炉不知最早起于何时，也许可以追溯到商周时代的青铜鼎。鼎用于烹煮肉食和祭祀，香炉里装的则是香料，都表达了对祖先和天地的尊敬。香炉真正的成型和发展，与印度佛教传入中国有千丝万缕的联系。在每日举行的敬佛礼佛的过程中，就包含了焚香的仪式，这使得焚香的习惯更广泛地进入到大众生活之中。到了宋代，焚香已经与烹茶、插花、挂画并列为当时生活中的“四艺”，成为文化活动中不可或缺的一项程式。宋代时，各种香炉除了供皇室、贵族和文人使用之外，也广泛出现在普通百姓的生活之中了。不但敬神祭祖要用香炉，在厅堂卧室里要点燃香炉，甚至在各种高端的宴会、欢乐的庆典上，也要焚香助兴，而一些小型香炉更是成为文人们随身携带的物品。比如宋代的《槐荫消夏图》，一个夏日的午后，一人在户外乘凉，慵懒地躺在槐荫之下，旁边的桌子上放着一只香炉，从他惬意的表情上，仿佛可以闻到空气里的清香。

    在汉朝，有一种“博山炉”已经在皇宫和贵族中流行了，炉体常用金属制作，呈青铜器中的容器豆的形状。炉子上面有高高尖尖的盖子，表面装饰着重叠雕刻的奇禽怪兽，象征传说中的海上仙山——博山，因此这种香炉就称作博山炉。后来，逐渐出现了青瓷或白瓷做的瓷香炉，香炉的样子也不再是单一的仙山了。李清照在《醉花阴》中写道，“薄雾浓云愁永昼，瑞脑销金兽”，这金兽便是做成动物造型的各式香炉。香炉是为了燃香取味，打造得小巧可爱，也可以装点室内陈设，这些金兽就有麒麟、狻猊、狮子、凫鸭、仙鹤等样子，看上去一定很萌。李清照这首词曲中的“瑞脑”，便是南宋文人焚香时用的香料了。汉朝时期博山炉都是有盖子的，应该是与燃香的原料和方式有关。在西汉之前，焚香用的都是屈原说的“兰芷变而不芳兮，荃蕙化而为茅”的茅香或蕙草，用法是将草放置在香炉中直接点燃。草叶燃烧后产生馥郁的香气，但有个毛病，就是烟火气比较大，烧太猛了还挺呛人的，所以得盖上盖子。

    汉朝之后，南海地区树脂类的龙脑香和苏合香传入，香料被制成香球或香饼，在下面放上炭火，高温将这些香料一点点烫燃起来，香味也很浓烈，烟火却少了很多，于是香炉在造型上获得了更多的发展空间，在做成金兽等造型之外，也出现了各种敞开式的香炉。香炉的广泛应用促进其自身在宋朝获得了大发展，宋代的皇帝都喜好复古，重视旧礼器，特别是宋徽宗最喜欢素雅娴静的釉色，加上宋代文坛中古文运动，也追求文以载道，反对浮靡的风气，素雅而简洁之美成为当时最流行的风尚。

    宋代重视金石之学，仿古蔚然成风。出现了各种青瓷仿制成商周青铜器的样子，而把它们缩小，便成了各种精致的敞开式小香炉，比如仿青铜鼎、鬲和樽的小香炉，还发展出高足杯式炉、敞口莲花炉、镂空覆盖式香炉，它们在生活中的应用更为广泛，可以方便地在室内移动，受到广泛的喜爱。

    于是，追求雅趣的李清照自然会喜欢上当时广泛流行的香炉了。她将自己的忧伤化作精致的悲情，投射到了一切美的事物上，香炉便与春花、微雨一起，成了李清照最喜爱的审美选择。但是你会发现，在李清照的词曲中，虽然香炉、香烟屡次出现，却从未提到香枝，在《槐荫消夏图》中，也只见香炉不见香枝插在里面。其实线香在明代才出现，在宋代，燃香常用的方法还不是直接点燃，而是透过炭火的焙烤而取其香气。因此我们在宋代绘画中只见形象各异的香炉，却看不到插在炉中的线香。

（选自方舒《李清照的香炉：沉香玉炉袅残烟》，有删改）