题干

19世纪末,英国科学家瑞利在对气体密度(通常在混合气体中,相对分子质量大的气体的体积分数越大,则混合气体的平均密度就越大)进行测定的工作中,发现以不同的N2进行测定时,会出现不能消除的微小误差,从而导致了稀有气体的发现。在实验中,瑞利利用了如下图所示的实验系统(箭头表示气体流向),通过的气体经过净化处理的纯氧气或空气。

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同类题4

    "Can I see my baby?" the happy new mother asked. When the baby was lying in her arms and she moved the cloth to look upon his tiny face, she gasped(吃力地喘着气). The doctor turned quickly and looked out of the hospital window. The baby had been born without ears. Luckily, time proved that the baby's hearing was perfect. Though the misfortune(不幸)happened to him, he grew into a handsome boy. Yet he felt ashamed when he communicated with others.
    "You should get in touch with other young people," his mother told him, with a kindness in her heart. The boy's father talked with the family doctor about his ears. "Could nothing be done?"the father asked. "I believe I could give him a pair of outer ears, if they could be got," the doctor replied.
    Two years went by. One day, his father said to the son, "You are going to the hospital, Son. Mother and I have someone who will donate the ears you need, but it's a secret."The operation is a big success. Later he married and entered the diplomatic(外交的) service. One day, he asked his father, "Who gave the ears? Who gave me so much? I could never do enough for him or her."
    "You could, my son," said the father, "but the agreement was that you are not to know…not yet."
    The years kept their secret, but one of the darkest days did come. He stood with his father over his mother's casket(棺材). Slowly, the father stretched forth(伸出) a hand and raised the thick, reddish brown hair to reveal the mother had no outer ears.
    "Mother said she was glad she never let her hair be cut," his father whispered gently, "and nobody ever thought mother less beautiful, did they?"

同类题5

阅读下文,根据要求回答问题。

竹篾①

左建明

    那是一个想来十分遥远的中午了,炽热的太阳高悬中天。

    我背了书包,在桉树的浓阴下轻捷地走着。由于南方雨水频繁,树阴下的通道长满了青青的苔藓。在道边上走,一不小心就摔个仰巴叉,于是,我只好在窄窄的通道中间走——但这不是我后来肇事的理由。

    接下来,我看见一位白发稀疏的老婆婆领着她的外孙在离我不到两丈远的地方蹒跚着前行。男孩儿的眼睛又黑又亮,可爱极了。他只穿了有个背带的开裆小裤衩,小屁股一撅一撅,跟个小鸭子似的。

    我还发现,他手里握了根又细又长的竹篾,那竹篾的尾端就在我脚前两三尺的地方游来摆去。这是一根充满诱惑与动感的美妙线条。

    那一会儿,我突然变得愚蠢可恶:我挪动着脚步,企图踩住那根美妙的竹篾。尽管我只是想跟那孩子逗着玩玩,但仔细想想,人的恶念原来与生俱有。

    我是终于将那竹篾踩住了。于是,美妙活泼富有生命力的竹篾一下绷直成一条僵硬毒辣的直线,与此同时,我听到那孩子哇的一声哭叫起来,我看见那根竹篾从他手里甩脱了,仿佛甩掉一条蛇。

    “啊呀!”老婆婆扳过孩子的手,不禁失声叫起来。我赶紧跑上去,一看,那孩子白胖胖嫩生生的小手被竹篾划了深深的一道伤口,鲜红的血往外涌流。我觉得心脏好像被竹篾一下子刺穿了,浑身打了一个永生难忘的激灵。

    那一刻,我惊慌失措,只盼着发生的事只是一个噩梦。

    老婆婆却说:“莫害怕,你又不是故意的。”

    我长吁一口气,内心的恐惧一下子被安抚了。因为老婆婆不以为我是故意的,我就可以免遭一场责难了。

    于是我就坡骑驴,顺水推舟,不管表情如何尴尬难堪,我极力装作不留心而误踩了竹篾的神态。是啊,竹篾那么长,后边的人不小心儿误踩上的可能性是挺大的呀!

    老婆婆急急惶惶地抱着孩子找卫生室去了。

    那条长长的竹篾刚才还活蹦乱跳着,这会儿却僵直地卧在长满苔藓的小路上。

    耳边还有那孩子渐远渐轻的哭声。

    午后,我被一种不安驱使着,到隔壁老婆婆家去看那孩子。孩子的手已经缠上了厚厚的白纱布,他的爸爸妈妈正心疼地皱着眉头。老婆婆见我去了,对小孩的爸妈说:“他不是故意的。都怪我,不该让娃儿拿篾子耍。”

    我低着头,对老婆婆充满感激,但我仍然没敢承认自己是故意的。

    那时候,我刚上初中,屈指算来,已有30年了。那条长竹篾为我培植了一种生理条件反射:无论何时何地,只要听到(更不用说见到)别人一不小心划破了皮肉,我立即会浑身打一个激灵,一种麻酥酥的感觉透遍全身,仿佛自己也挨了一刀。

    那仅仅是一种生理条件反射吗?

    多少年来,我眼前常常浮现出一幅美丽生动的图画:一位白发老婆婆领着她的胖嘟嘟的小外孙在前面走,那孩子拖着一条长长的竹篾,在他一撅一撅的屁股蛋后边活蹦乱跳地游来摆去。

    我干吗要踩上一脚啊?

(选自《走过心灵的脚步没有声音》)

【注释】①竹篾:竹子劈成的薄片。