人由小长大是与人体细胞的生长和分裂分不开的．人体细胞核中有46条染色体，经过两次分裂形成了四个细胞，每个细胞中染色体数目是（ ）
A．92条
B．46条
C．23条
D．数目不定
细胞的分裂过程中染色体的变化：细胞分裂时，染色体变化最明显．染色体会进行复制，细胞分裂过程中，染色体均分成完全相同的两份，分别进入两个新细胞中．也就是说，两个新细胞的染色体形态和数目相同，新细胞与原细胞染色体形态和数目也相同．由于染色体内有遗传物质DNA，因此，新细胞与原细胞所含的遗传物质是一样的．每一种生物细胞核内染色体的形态和数目都是一定的，如人的体细胞中含有46条（23对）染色体，经过两次正常分裂形成了四个细胞，每个细胞中染色体数目是46条．
故选：B．
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| A young student was one day taking a walk with a professor, who was commonly __1__ the students' friend. As they went __2__, they saw lying in the path a pair of old __3__, which were supposed to belong to a poor man who was working in a __4__ close by. The student turned to the professor, saying, "Let's play the man a __5__: We will hide his shoes, and __6__ ourselves behind those bushes, and wait to see his __7__ when he cannot find them." "My young friend," answered the professor, "we should never __8__ ourselves at the __9__ of the poor. But you are __10__, and you may give yourself a much greater __11__ by means of the rich man. Put a coin into each shoe, and then we will hide ourselves and __12__ how the discovery affects him." The student did so, and they both placed themselves behind the bushes. The poor man soon finished his work, and came __13__ the field to the path __14__ he had left his coat and shoes. While __15__ his coat he slipped his foot into one of his shoes; but feeling something __16__, he bent down to feel __17__ it was, and found the coin. Astonishment and wonder were seen upon his face. He then looked around him on all sides, but no person was to be seen. He now put the money into his pocket, and continued to put on the other shoe; but his __18__ was doubled on finding the other coin. He fell upon his knees, looked up to heaven and said aloud a fervent (热诚的) thanksgiving, in which he __19__ his wife, sick and helpless, and his children without bread. The student stood there deeply __20__, and his eyes were filled with tears. | ||||
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