题干

下列关于基因突变的说法正确的是(    )

A:如果显性基因A发生突变,只能产生等位基因a

B:通过人工诱变的方法,人们能培育出生产人胰岛素的大肠杆菌

C:基因突变都可以通过有性生殖传递给后代

D:基因突变是生物变异的根本来源,有的变异对生物是有利的

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答案(点此获取答案解析)

D

同类题4

阅读下面短文,掌握其大意,然后从每题所给的A、B、C、D四个选项中选出最佳选项

    One morning, when I was leaving for my business, a middle-aged man came up and asked me for help. He said he had no 1 to get food for his large family.

    You look 2. Why don't you work?" I asked." Simply because I cannot get work,sir.""If I give you work, what you want?" "3 I can get bread for my family, sir." he answered.

    I decided to find out if he  4 meant what he said. "OK. I'll give you one pound an hour, if you will 5   a brick(砖)under your arm and walk around the square for five hours without stopping. ""Thank you, sir. I will. "

    I found a brick and started him on his walk before I went to my 6. I never thought he would he had 7.

    When I came back five hours later, I saw him 8 walking, with the brick under his arm.

    I stopped him and gave him 9 pounds. He thanked me and told me that some people had 10 to help him when they knew why he was doing all this. He would go and ask 11 for work. Before leaving, he asked if I would give him the 12.I did.

    Several years later, a well-dressed man greeted me on a train. Seeing I was not sure who he was, he 13 that he was the brick man and had his own business now. "You know, I still keep that brick and always value it as the most 14 thing I have as it has brought me luck and success."

    15, it was not the brick that made the man successful, but his faithfulness(坚定) in doing even a very little thing.