题干

鸡的性别受性染色体控制,公鸡的性染色体组成为ZZ,母鸡的性染色体组成为ZW。在鸡中,羽毛的显色需要显性基因C存在,基因型cc的为白色。已知鸡的芦花斑纹由Z染色体上的基因B控制,一只基因型为ccZbW的白羽母鸡跟一只芦花公鸡交配,子一代都是芦花,如果子代个体相互交配。理论上,后代表现型分离比应是
①后代中公鸡和母鸡之比为:1∶1   ②芦花鸡中公鸡和母鸡之比为:2∶1
③公鸡中芦花和白羽毛之比为:3∶1 ④母鸡中芦花、非芦花、白羽之比为:3∶3∶2

A:①③

B:②④

C:①②③

D:①②③④

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D

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完形填空
       Once upon a time there was a little orphan(孤儿) who always wished that he could fly like a bird. It was very   1   for him to understand why he could not fly.
  There was another little boy who was crippled(瘸子). One day the orphan came to a park, where he saw the little crippled boy   2   in the sand alone.
  He ran over to the little crippled boy and asked him if he had ever wanted to fly like a bird.
  “No, ” he said. “  3  I've been thinking about what it would be like to walk and run like   4  .”
  “That is very sad, ” said the little orphan. “Do you think we could be friends?”
  “Sure, ”said the little crippled boy.
  The two little boys played for hours.  5 of them felt as lonely as they have been before. Then the little crippled   6 father came with a wheelchair to  7  his son. The little orphan ran over to him and said something into his ear.
  “That would be Okay, ”said the man.
  The little orphan ran back to his friend and said, "You are my only friend and I   8 I could do something to make you walk and run like others. 9  , I can't. But there is something that I can do for you."
  The little orphan boy turned10  and told his friend to slide onto his back. Then he began to run across the grass. He ran faster and faster,  11 the little crippled boy on his back.
The father began to cry with tears as his son shouted at the top of his   12 , "I am FLYING! Daddy, I am FLYING!"
That's the little orphan who helped the crippled boy  13 the dream to fly in his life and moved the father.14 he didn't know the reason why he could not fly, he helped another boy fly and harvested happiness from it. Let's always be ready to help others because helping others is helping   15 .