题干

如图环状DNA(质粒A)上含抗氨苄青霉素和四环素抗性基因.现将人的生长激素基因由a点切开嫁接到质粒A上形成重组质粒,将重组质粒导入细菌B并获取“工程菌”进行培养.结果人的生长激素基因及抗氨苄青霉素基因都能成功表达,而四环素抗性基因不能表达.这一事实说明(   )

A:基因能控制生物的性状

B:基因是控制生物性状的基本单位

C:基因是有遗传效应的DNA片段

D:DNA是主要的遗传物质

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B

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       As I rushed among the tables, suddenly, a  1  asked if I could mind a child. I was quite   2 but I could tell the man was quite desperate. So I had to make a  3  with him that if he wanted his son to stay and wait for him, he had to 4  something in the shop.

       This was quite  5  for the man to do; I could  6  he was quite poor by the  7  he was dressed. It looked as if he had tried to come in his 8 clothes. But they still looked a bit old and worn out 9 he had often worn them, just to make himself look best. Looking down I could see his 10  were also a bit torn and the heels were in a terrible state. I thought he was going for a job interview. In the end he bought a small box of 11 for his little son and seated him down in the corner. I could tell the boy was feeling down and only could   12  with a bit of cheering up.

       Seeing that the kid sat there for quite a while, I was a bit  13  as the poor little kid was sitting  14  his own. People watched him and some kids even came over to pick on him. I was15  to see one of them even knocked his cookies off the table.He quickly went and got them back without saying a word.I was hoping his father would 16  up and come back for his son's 17  .

        At closing time, the only person left was the little boy.After a while, the father finally came in with a tiresome look. I  18 he didn't get any job.As they were leaving, I offered the kid a little cake, but the man rejected it. I19  he felt as if I had just abused him.Of course I didn't mean to.But I could understand why he felt like that.I only wished them good  20  whatever happened.

The man opened the door to leave-father and son hand in hand.