题干

肺炎双球菌的A基因含有A1~A77个小段,科学家分离出此细菌A基因的4个缺失突变株:J(缺失A4、A5、A6)、K(缺失A3、A4)、L(缺失A4、A5、A6、A7),M(缺失A1、A2、A3、A4、A5).将一未知的突变株X与J或L共同培养,可以得到转化出来的野生型细菌(即7个小段都不是突变型)。若将X与K或M共同培养,得到转化的细菌为非野生型,由此可判断X的突变位于A基因的哪一小段(   )

A:A2

B:A3

C:A4

D:A5

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答案(点此获取答案解析)

B

同类题4

阅读下面的文言文,完成下列各题。

    (董)文用字彦材,(董)俊之第三子也。世祖在潜藩,命文用主文书,讲说帐中,常见许重。世祖即位,建元中统。阿术奉诏伐宋,召文用为其属,文用辞曰:“新制,诸侯总兵者,其子弟勿复任兵事。今吾兄文炳以经略使总重兵镇山东,我不当行。”阿术曰:“潜邸旧臣,不得引此为说。”文用谢病不行。至元改元,召为西夏中兴等路行省郎中。时诸王只必铁木儿镇西方,其下纵横需索无算省臣不能支文用坐幕府辄面折以法其徒积忿谮文用于王。王怒,召文用,使左右杂问之,文用曰:“我天子命史,非汝等所当问。”王即遣其傅讯文用。文用谓之曰:“我汉人,生死不足计。所恨者,仁慈宽厚如王,以重戚镇远方,而其下毒虐百姓,凌暴官府,伤王威名,于事体不便。”因历指其不法者数十事。其傅惊起,去白王,王即召文用谢之曰:“非郎中,我殆不知。郎中持此心事朝廷,宜勿怠。”自是谮不行而省府事颇立。会初得江南,图籍、金玉、财帛之运,日夜不绝于道,警卫输挽,日役数千夫。文用忧之曰:“吾民弊矣,而又重妨耕作,殆不可。”乃从转运主者言:“州县吏卒,足以备用,不必重烦吾民也。”主者曰:“汝言诚然,万一有不虞,则罪将谁归!”文用即手书具官姓名保任之。民得以时耕,而运事亦不废。二十七年,隆福太后在东宫,以文用旧臣,欲使文用授皇孙经,具奏上,以帝命命之。文用每讲说经旨,必附以朝廷故事,丁咛譬喻,反复开悟,皇孙亦特加敬礼。是岁,世祖崩,成宗将即位上都。帝在东宫时,正旦受贺,于众中见文用,召使前曰:“吾向见至尊,甚称汝贤。”辄亲取酒饮之。至是,眷赉益厚。大德元年,上章请老,六月戊寅,以疾卒,年七十有四,谥忠穆。

(节选自《元史•列传三十五》)

同类题5

根据短文理解,选择正确答案。

    If women are mercilessly exploited(剥削)year after year,they have only themselves to blame.Because they tremble at the thought of being seen in public in clothes that are out of fashion,they are always taken advantage of by the designers and the big stores.Clothes which have been worn only a few times have to be put aside because of the change of fashion.When you come to think of it,only a woman is capable of standing in front of a wardrobe(衣橱)packed full of clothes and announcing sadly that she has nothing to wear.

    Changing fashions are nothing more than the intentional creation of waste.Many women spend vast sums of money each year to replace clothes that have hardly been worn.Women who cannot afford to throw away clothing in this way,waste hours of their time altering(政变)the dresses they have.Skirts are lengthened or shortened;neck-line are lowered or raised,and so on.

    No one can claim that the fashion industry contributes anything really important to society.Fashion designers are rarely concerned with vital things like warmth,comfort and durability(耐用).They are only interested in outward appearance and they take advantage of the fact that women will put up with any amount of discomfort,as long as they look right.There can hardly be a man who hasn't at some times in his life smiled at the sight of a woman shaking in a thin dress on a winter day,or delicately picking her way through deep snow in high-heeled shoes.

    When comparing men and women in the matter of fashion,the conclusions to be drawn are obvious.Do the constantly changing fashions of women's clothes,one wonders,reflect basic qualities of inconstancy and instability (不稳定)?Men are too clever to let themselves be cheated by fashion designers.Do their unchanging styles of dress reflect basic qualities of stability and reliability(可靠)?That is for you to decide.