题干

下列有关生物知识的叙述中,正确的说法有几项(  )

①自然条件下,基因重组通常发生在生殖细胞的形成过程中;

②非同源染色体上某片段的移接,仅发生在减数分裂过程中;

③同卵双生兄弟间的性状差异是基因重组导致的;

④基因中一个碱基对发生改变,则生物的性状一定发生改变;

⑤在镜检某基因型为AaBb的父本细胞时,发现其基因型变为AaB,此种变异为基因突变.

A:1项

B:2项

C:3项

D:4项

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答案(点此获取答案解析)

A

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The Broken Lantern

    On a wild July night, the storm was getting worse and worse. Kate Shelley, who lived between Honey Creek(小溪) and Des Moines River, was1looking out of the window, wondering2it would wash away the bridges over them, when suddenly came the loud3of breaking wood, then followed by a great splash(飞溅的水花). She realized the bridge over the creek was4. At that time, the midnight train was almost due. If no one told the engineer to5the train, it would fall into the creek with a hundred or more6. The situation was so urgent that Kate7to go to Moingon Railway Station to get help. Immediately she8out into the storm with her father's railway lantern.

    Moingon lay on the far side of Des Moines River. The only way to get there was to cross a long wooden railroad bridge. Even in the daytime, it was9to walk on it because there was no foot walk or railing(栏杆) except only rails and ties. The ties were 10enough apart for the girl to fall through.

    Kate stopped when she came to the 11  She had never seen the river rising so high that she was 12  Her father had been killed in a train accident by that river and her brother had drowned there. But she soon managed to 13thinking more of the past happenings for she knew that train had to be stopped14it was too late. She started to step on that dangerous bridge, knowing she might fall into the rush water at any moment. What's worse, she broke her lantern while making her way, exposing herself to the 15  She had to climb on her hands and knees…It seemed like a long time. At last she 16the other side. She stopped just long enough to catch her breath. Then she ran 17to the railway station. When she finally got there, she was out of 18  wet all over, her hat blown away, her hands and knees still bleeding and her eyes looking 19. She told the station man what had happened to the Honey Creek Bridge before her fainting. Finally, the passengers were saved. The girl's heroic deed was rewarded. For her 20act, Kate enjoyed a right of getting on or off the train at her door when she wanted.