题干

下图1中的噬菌斑(白色区域),是在长满大肠杆菌(黑色)的培养基上,由一个T2噬菌体侵染细菌后不断裂解细菌产生的一个不长细菌的透明小圆区,它是检测噬菌体数量的重要方法之一。现利用培养基培养并连续取样的方法,得到噬菌体在感染大肠杆菌后数量的变化曲线(下图2),下列叙述错误的是(  )

A:培养基中加入含35S或32P的营养物质,则放射性先在细菌中出现,后在噬菌体中出现

B:曲线a~b段,细菌内正旺盛地进行噬菌体DNA的复制和有关蛋白质的合成

C:曲线b~c段所对应的时间内噬菌体共繁殖了10代

D:限制c~d段噬菌斑数量增加的因素最可能是绝大部分细菌已经被裂解

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答案(点此获取答案解析)

C

同类题2

阅读理解。

    I arrived at my mother's home for our Saturday family dinner. The smells of food flew over from the kitchen. Mother was pulling out quilt after quilt from the boxes, proudly showing me their beauties. I knew they were all made herself. She was preparing for a quilt show on TV. When we began to fold and put them back into the boxes, I noticed something at the bottom of one box. I pulled it out. “What's this?” I asked.

“Oh?” Mom said, “That's Mama's quilt.”

    I spread the quilt. It looked as if a group of school children had made the pieces together.

 “Grandmother made this?” I asked in surprise. My grandmother was a master at making quilts. This certainly didn't look like any of the quilts she had made.

  “Yes, right before she died. I brought it home with me last year and made some changes,” Mom said, “I'm still working on it. See, this is what I've done so far.”

     I looked at it more closely. She had made a line straight(直的). At the center of the quilt, she had stitched a piece of cloth with these words:    “My mother made many quilts. She didn't get all lines straight. But I think this is beautiful. I want to see it finished. Her last quilt.”

“Oh, this is so nice, Mom.” I said. I was sure now that by completing my grandmother's quilt, my mother was honoring her own mother. I realized that I held in my hands a family treasure. It started with the loving hands of one woman, and continued with the loving hands of another.