问题 单项选择题

继发性咬合创伤的形成主要是()

A.牙周支持力不足

B.力过大

C.牙齿排列不齐

D.反

E.不良修复体有高点

答案

参考答案:A

解析:

因牙周支持力不足,对原正常大小的咬合力不能承受,造成牙周组织的病理性改变。称为继发性咬合创伤。

完形填空

阅读下面短文并回答问题,然后将答案写在横线上(请注意问题后的词数要求)

[1]Everyone wants something in life, love, money, success and so on. Yet too many people fail to achieve their goals, and nearly all of them are for the same reason.

[2]It‘s true that terrible things do happen to people during their lives, though no fault of their own, which may make them feel upset. Generally speaking, however, getting what you really want out of life is just a matter of the following three simple steps.

[3]Firstly, you have to decide what it is you want the most. But do not make a list of wishes; try to focus on one thing at a time. If you‘re not sure about where you want to go, you‘d better think it over first and not hurry to perform.

[4]Secondly, create an action plan. This will be your map for getting from ”____________________” to ”where you want to go”. You know what you want, and what steps you are going to take to get it. For example, if you want a better job, start with a skills assessment and maybe some extra training. Then you‘ll need to sell yourself and your skills either to your present employer or to a new employer.

[5]Other goals will require a bit more thought. Some will really get you lost without a clue of how to get there. Not to worry, though, books, biographies and such, can be of great help.

[6]The third and final step is to execute. Do what you planned. Take the steps you outlined on your road map and keep going on all the time. If you run into some people who are against you, simply ignore them.

[7]Never give up the goal. Keep pushing. Whatever you do, do not lose heart until you have what you desire in your hands. Never think that you can’t turn your dream into a reality.

小题1:What does the author want to tell readers in this article? (No more than 10 words)

_________________________________________________________________

小题2:Fill in the blank in Paragraph 4 with proper words. (No more than 5 words)

__________________________________________________________________

小题3:list the three simple steps that you should take if you want to achieve your goals.(no more than 20 words)

小题4:What’s the most important thing when deciding what to do? (No more than 8 words)

___________________________________________________________________

小题5:What does the underlined word “it” in paragraph 3 probably refer to? (No more than 5 words)

___________________________________________________________________ 

单项选择题

斯坦福大学的科学家们制造出了一种分子扩大了的DNA,其双螺旋结构比自然界已发现的任何一种DNA都要宽。这种大分子DNA不仅耐热性好,而且还能在黑暗中发光——这一特性可能对检查人体基因缺陷十分有用。
DNA的典型形态是双螺旋结构——两组平行的基因信息像一根长长的盘旋的梯子一样联结在一起。每一节梯子都由两个互补的碱基组成,它们组合在一起成为碱基对。
自然界只有4种天然碱基,它们是:腺嘌呤(A),鸟嘌呤(G),胞嘧啶(C),胸腺嘧啶(T)。由于4种碱基各自独特的形态和大小,T常常与A配对,G常常与C配对。其他的配对形式(如A配C,G配T)都会因为太宽或太窄而不能形成双螺旋结构。
人类DNA由约30亿个碱基对按特定顺序排列组成,它们将人类健康生存所需要的基因信息拼写出来。只要一两对碱基对的排列顺序出错,基因密码就会出现混乱,从而导致婴儿在出生时会出现可怕的畸形或导致像癌症和镰状细胞贫血症这样的疾病。
加利福尼亚理工学院的化学家纳尔逊·伦纳德在20世纪70年代做过一个实验,他将一个苯环嵌入碱基A,得到了一个大碱基xA,xA比普通碱基A宽了约33%。斯坦福大学的科尔和他的同事们继续了伦纳德的实验。
斯坦福大学的这个研究组使用与伦纳德相似的方法得到了xT——一种大小为自然T两倍的合成碱基。接下来的挑战是将这些大碱基嵌入双螺旋结构。
他们通过将xA与自然T组合,xT与自然A组合,从而合成了完美的双螺旋结构。一种比自然DNA宽了约20%的新的稳定的DNA形态诞生了,研究人员将它命名为“扩展DNA”或“xDNA”。
研究人员发现xDNA有几个比自然DNA更加优良的特点。比如说,xDNA比自然DNA的耐热性好。在实验室环境下,自然DNA的分解温度是21.3摄氏度,而xDNA在55.6摄氏度时还依然保持完整。
科尔说:“一般说来,体积大的物体比体积小的物体耐热性好,DNA也不例外。”
他补充说,大一些的分子一般会发出荧光,这也许能解释为什么自然DNA不发光,而xDNA却发出一种紫色光,使它在显微镜下被看得很清楚。
在自然界,DNA携带了所有的遗传信息并传给后代。科尔正在研究xDNA是否也有这种功能。
不过他警告说:“这种新的DNA不太可能在地球上的自然环境中发挥功能,因为它太大了。不过,我们希望,有一天它会成为地球上或是其他星球上的一种新的生命形式的基因物质,这样当我们往其他星球上派探测机器人时,我们就会知道要在冰层下寻找什么样的生命形态。”

根据原文提供的信息,以下推断不正确的一项是______。

A.一般说来,体积大的物体比体积小的物体耐热性好,这一规律可以解释xDNA比自然DNA耐热性更好的现象
B.大一些的分子一般会发出荧光,DNA也不例外,这就可用来解释xDNA与自然DNA在发光问题上的差异
C.因为xDNA太大了,科尔认为它在地球上的自然环境中发挥功能的可能性不大
D.如果xDNA将来能成为地球上或是其他星球上新的生命形式的基因物质,它就会为我们的太空生命探索提供指导