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问题 填空题

女性产生的一个卵细胞中所含的性染色体是______，男性产生的一个精子中所含的性染色体是______．

答案

在形成生殖细胞的过程中，成对的染色体分开，每对染色体中的一条进入精子或卵细胞中；女性的体细胞内的染色体组成是22对常染色体+一对性染色体XX，因此女性产生的卵细胞中的染色体组成是22条常染色体+X性染色体，即女性产生的卵细胞中含有的性染色体是X．男性的体细胞内的染色体组成是22对常染色体+一对性染色体XY，因此女性产生的卵细胞中的染色体组成是22条常染色体+X或Y性染色体，即男性产生的卵细胞中含有的性染色体是X或Y．

故答案为：X；X或Y．

听力题

阅读下面短文，并借助上下文和插图补充所缺信息。每个空只能填写一个意义相符、形式正确的单词。并将答案填写在答题卡相应题目的答题位置上。

Li Ming is a middle school student. His 15th birthday is coming on  小题1: 3rd. One day, Li Ming walked past the shoe shop at the street corner. Once again, he stopped to look at the shop  小题2:. He felt happy to see the shoes that he wanted very much were still there. He really wanted to have   小题3: for his birthday. Looking down at his old shoes, he felt sorry for himself.

He sadly walked away and thought   小题4: to tell his mother about it. He knew she would give him  小题5:  he liked if she could. But he also knew very well she had little money for that￥1299-Nike Shoes. He   小题6:  not to go home at once, as he didn’t want to upset his mother. So he went to the park and sat on the   小题7: . There he saw a girl in a wheel chair. He noticed that the girl  小题8: the wheel with her hands. Li Ming watched her carefully and was  小题9: to find that the girl had no feet. He looked at his own feet, “It’s much  小题10: to be without shoes than without feet.” He thought. There was no reason for him to feel so sorry and sad. He went away and smiled, thinking he was luckier.

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单项选择题

市场失灵是指( )。

A．由于市场存在不完全性导致市场经济作用被削弱的现象
B．由于生产要素富有流动性导致市场经济作用被加强的现象
C．由于巨大外部性的存在导致市场经济作用被加强的现象
D．政府制定和执行的政策扭曲了环境和资源使用的真实成本所导致的环境污染和破坏
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