题干

正常情况下,图中A细胞与其分裂成的a、b两细胞中染色体数目的关系是(  )

A:a、b中的染色体数目均是A中的两倍

B:a、b中的染色体数目均与A中的相等

C:a、b中的染色体数目均是A中的一半

D:a、b中的染色体数目均与A中的不相等

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答案(点此获取答案解析)

B

同类题1

【历史上重大改革回眸】

阅读下列材料,回答问题。

材料一  自建国至嘉庆十二年(1644—1807年)160多年的时间里,清朝白银对制钱的比价一般在1000文以下,1808年以后近半个世纪的时间里,银钱比价持续上涨。银价的上涨意味着广大劳动者必须付出更多的铜钱(完税)……1845年银价上涨更甚,御史刘良驹奏称:“银价之昂未有甚于今日者,京中纹银每两易制钱乃二千文,外省则每两易制钱二千二三百文不等”,而且“其势日就增加,尚无底止”。鸦片战争后10年间,全国各地农民起义此起彼伏。由于对外贸易的发展,更多的外国银元流入中国社会,外商趁机用成色较低的银元套购中国纹银运往国外,制成银元后返销中国牟取暴利。

——摘编自许弘《近代中国银货币改革述论》

材料二  林则徐于1833年提出自铸银元。光绪初年,吉林省首先用机器试铸银币。1889年,两广总督张之洞才获准在广东设造币厂。此后,湖北、江苏等省纷纷仿效。1905年,清政府开始全面进行货币改革,目的是统一银币。但由于本位币不定,引起了“两”“元”之争。焦点是用“两”还是用“元”,以湖广总督张之洞、直隶总督袁世凯为代表的“一两”银币派认为各国应有自己的币制体系,中国不能亵渎国体而丧失主权……1910年,清政府颁布《币制则例》,自此,两元之争落下帷幕。……1911年,停止各省自由铸造,铸币权统归中央。……辛亥革命爆发,清政府灭亡,银币没有来得及正式发行。

——摘编自刘士刚《晚清的货币政策》

同类题3

阅读理解

    No one is sure how the ancient Egyptians built the pyramids near Cairo. But a new study suggests they used a little rock‘n'roll. Long-ago builders could have attached wooden pole s to the stones and rolled then across the sand, the scientists say.

     “Technically, I think what they're proposing is possible,” physicist Daniel Bonn said.

    People have long puzzled over how the Egyptians moved such huge rocks. And there's no obvious answer. On average, each of the two million big stones weighed about as much as a large pickup truck. The Egyptians somehow moved the stone blocks to the pyramid site from about one kilometer away.

    The most popular view is that Egyptian workers slid the blocks along smooth paths. Many scientists suspect workers first would have put the blocks on sleds(滑板). Then they would have dragged them along paths. To make the work easier, workers may have lubricated the paths either with wet clay or with the fat from cattle. Bonn has now tested this idea by building small sleds and dragging heavy objects over sand.

    Evidence from the sand supports this idea. Researchers found small amounts of fat, as well as a large amount of stone and the remains of paths.

    However, physicist Joseph West thinks there might have been a simpler way , who led the new study . West said , “I was inspired while watching a television program showing how sleds might have helped with pyramid construction . I thought , ‘Why don't they just try rolling the things?'“A square could be turned into a rough sort of wheel by attaching wooden poles to its sides , he realized . That , he notes , should make a block of stone” a lot easier to roll than a square”.

    So he tried it.

    He and his students tied some poles to each of four sides of a 30-kilogram stone block. That action turned the block into somewhat a wheel. Then they placed the block on the ground.

    They wrapped one end of a rope around the block and pulled. The researchers found they could easily roll the block along different kinds of paths. They calculated that rolling the block required about as much force as moving it along a slippery(滑的)path.

    West hasn't tested his idea on larger blocks, but he thinks rolling has clear advantages over sliding. At least, workers wouldn't have needed to carry cattle fat or water to smooth the paths.