题干

我国制造的C919 大飞机采用的复合材料中使用了高温陶瓷材料氮化硅(Si3N4).下列说法正确的是(   )

A:Si3N4中N 为-3价,Si为-4 价

B:Si3N4中Si和N的质量比为3:2

C:Si3N4中含2 个氮分子

D:Si3N4中氮元索的质量分数最大

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答案(点此获取答案解析)

B

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    We could all say that we have bad days as we go through life, but what does it take to have a really good day?

    I remember a day recently when I had to go to the 1 for special tests because I wasn't feeling well and my doctor sent me to a specialist to try and find the cause of my illness.

    As I 2 to the hospital, I was feeling sad and certainly wasn't on top of my game. As I got to the hospital, I began my 3 for a parking lot. I finally found one not too far from the entrance to the hospital.

    As I got out and brought my change out of my pocket, I noticed a man looking a little 4 standing in front of a parking meter (停车记时收费表) two cars away. He seemed to be searching his pockets for what I supposed were 5 for the meter.

    Although I 6 didn't feel that great, I thought that I should at least go over to him and find out if I could 7 him. As I stood beside him, he turned to me looking worried. I asked him if he had a problem I could help with. He said that he had no coins at all because he was only thinking about visiting his sick wife when he left his house.

    I reached into my pocket and 8 out two dollars and gave it to him without saying a word. And, without waiting for a reply, I turned on my heel and said to him as I was walking away: “Have a good day.”

    The funny thing was that I felt a lot brighter, a small smile came to my face, and I seemed to walk just a little quicker. I was walking away when he called out: “Thank you so much.” You know, I didn't even 9 him to say anything. He didn't have to say a word to me. It was simply enough to know that I had helped someone else who needed a little10. That's all it took to bring a smile to my face as I went on toward completing my own business.

    You know, it doesn't take much to help someone else.

同类题5

阅读短文,回答问题。

    这天,一个喝醉了的驾驶者,以六十英里的速度,对准树干撞去。于是人死。于是交通专家宣判那树要偿命。于是这一天来了,电锯从树的踝骨咬下去,嚼碎,撒了一圈白森森的骨粉。那树仅仅在倒地时呻吟了一声。这次屠杀安排在深夜进行,为了不影响马路上的交通。夜很静,像树的祖先时代,星临万户,天象庄严,可是树没有说什么,上帝也没有。一切预定,一切先有默契,不在多言。与树为邻的一位老太太偏说她听见老树叹息,一声又一声,像严重的哮喘病。伐树的工人什么也没听见,树缓缓倾斜时,他们只发现一件事:本来藏在叶底下的那盏路灯格外明亮,马路豁然开旷,像拓宽了几尺。

    尸体的肢解和搬运连夜完成。早晨,行人只见地上有碎叶,叶上每一平方厘米仍绿着。它果然绿着生,绿着死。缓缓的,路面染上旭辉;缓缓的,清道妇一路挥帚出现,她们戴着斗笠,包着手臂,是树的亲戚。扫到树根,她们围着年轮站定,看那一圈又一圈的风雨图,估计根有多大,能分裂成多少斤木柴。一个说,昨天早晨,她扫过这条街,树仍在,住在树干里的蚂蚁大搬家,由树根到马路对面,流成一条细细的黑河。她用作证的语气说,她从没有见过那么多蚂蚁,那一定是一个蚂蚁国。她甚至说,有几个蚂蚁像苍蝇一般大。她一面说,一面用扫帚划出大移民的路线,汽车的轮胎几次将队伍切成数段,但秩序毫不紊乱。对着几个睁大了眼睛的同伴,她表现出乡间女子特有的丰富见闻。老树是通灵的,它预知被伐,将自己的灾祸先告诉体内的寄生虫。于是弱小而坚忍的民族,决定远征,一如当初它们远征而来。每一个黑斗士在离巢后,先在树干上绕行一周,表示了依依不舍。这是那个乡下来的清道妇说的。这就是落幕了,它们来参加树的葬礼。

    两星期后,根也被挖走了,为了割下这颗生满虬须的大头颅,刽子手贴近它做了个陷阱,切断所有的动脉静脉。时间仍然是在夜间,这一夜无星无月,黑得像一块仙草冰。他们带利斧和美制的十字镐来,带工作灯来,人造的强光把举镐挥斧的影子投射在路面上、在公寓二楼的窗帘上,跳跃奔腾如巨无霸。汗水超过了预算数,有人怀疑已死未朽之木还能顽抗。在陷阱未填平之前,车辆改道,几个以违规为乐的摩托车骑士跌进去,抬进医院。不过这一切都过去了。现在,日月光华,周道如砥,已无人知道有过这么一棵树,更没有人知道几千条断根压在一层石子一层沥青又一层柏油下闷死。