题干

质粒是基因工程中最常用的运载体,它存在于许多细菌体内.质粒上有标记基因如图所示,通过标记基因可以推知外源基因(目的基因)是否转移成功.外源基因插入的位置不同,细菌在培养基上的生长情况也不同,如表是外源基因插入位置(插入点有a、b、c),请根据表中提供细菌的生长情况,推测①②③三种重组后细菌的外源基因插入点,正确的一组是(  )

细菌在含青霉素培养基上生长情况

细菌在含四环素培养基上生长情况

能生长

能生长

能生长

不能生长

不能生长

能生长

A:①是c;②是b;③是a

B:①是a和b;②是a;③是b

C:①是a和b;②是b;③是a

D:①是c;②是a;③是b

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答案(点此获取答案解析)

A

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阅读下列短文,从下面每题的A、B、C、D四个选项中选出最佳答案。

    Just as I entered my house, I heard a sound coming from the bedroom upstairs — it was from myJust as I entered my house, I heard a sound coming from the bedroom upstairs — it was from my favourite violin.

    “Thief!”

    I rushed upstairs and saw a boy in dirty clothes pulling my violin down. At first sight, I found a new pair of shoes missing. It seemed he was surely a thief.

    However, when I saw his eyes full of fear, my anger disappeared. I smiled and asked, “Are you Mr. Ram's student Rubens? I'm his butler(男管家). I've heard Mr. Ram said his student would come. It must be you.”

    “Has my teacher gone out?” the boy said, “I think I'd better visit him again in a while.”

    I nodded and asked him, “Do you like playing the violin?”

    “Yes, but I'm too poor to afford one.” the boy replied. 

    “Then, I'll give you this violin.” The boy looked at me in surprise, but he picked up the violin. While going out of the room, he suddenly saw a huge photo of me playing the violin at the Grand Theatre of Sydney on the wall. His face turned pale. He stood there for a moment and ran out. He must have understood what had happened because no master would put up the butler's photo on the wall of his living room.

    A few years later, at a music competition in Melbourne, I was invited to be the judge. Finally, a violin player called Merritt won the first prize.

    After the prize-giving, Merritt ran to me holding a violin box, his face red, and asked, “Mr. Brian, do you still know me? You gave me this violin, which I have treasured ever since! Today, I want to say sorry and give back the violin to you without regret…”

    He was just the “Mr. Ram's student”!