题干

如图是按顺时针方向表示的4种植物细胞的细胞周期,其中说法不正确的是(    )

A:图中的b→a→b表示细胞增殖过程的一个细胞周期

B:甲图的b→a与丙图的b→a所用的时间可能一样长

C:从a→b,DNA含量增加一倍;遗传物质平分发生于b→a段

D:观察植物细胞有丝分裂的最好材料是植物丁

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A

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    Katie was in big trouble.She was such a sweet kid; a third-grade teacher always dreamed of having a classroom filled with Katies, she was never ever a discipline(纪律) problem. I just couldn't imagine why she had made her parents so angry.

    It seemed that Katie had been spending money in the lunchroom. Her parents explained that Katie brought a great homemade lunch each day, and there was no reason for her to buy school lunch. They wondered why but failed.So they asked me to help them get to the bottom of this situation.

    The next day, I asked Katie to my office. “Why are you buying lunches, Katie? What happened to your homemade lunch?” I asked. “I lose it,” she replied. “I don't believe you, Katie. Is someone stealing your lunch, Katie?” I asked. “No. I just lose it,” she said.Well, there was nothing else I could do.

    The problem was still unsolved the next week when I noticed a boy who was new to the school sitting alone at a lunch table. He always looked sad and scared. I thought I would go and sit with him for a while. As I walked towards him, I noticed the lunch bag on the table. The name on the bag said “Katie”.

    Now I understood and I talked to Katie. It seemed that the new boy never brought a lunch, and he wouldn't go to the lunch line for a free lunch. He had told Katie his secret and asked her not to tell anyone that his parents wanted him to get a free lunch at school. Katie asked me not to tell her parents, but I drove to her house that evening after I was sure that she was in bed. I had never seen parents so proud of their child.

    Katie still buys lunch every day at school. And every day, as she heads out of the door, her  mom hands her a delicious homemade lunch.