题干

下列关于DNA分子结构的叙述,不正确的是(    )

A:—般情况下,每个DNA分子含有四种脱氧核苷酸

B:每个DNA分子中,都是碱基数等于磷酸数等于脱氧核苷酸数等于脱氧核糖数

C:一段双链DNA分子中,若含有30个胞嘧啶,会同时含有30个鸟嘌呤

D:每个脱氧核糖均只与一个磷酸和一个含氮碱基相连

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答案(点此获取答案解析)

D

同类题5

阅读短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项。

    Many kids don't drink enough water daily, according to a new study. The study's lead author, Erica Kenney, at first planned to look into the amount of sugary drinks kids were drinking in schools. However, during her research she found that many kids were simply not drinking enough water.

    Kenney and her team examined data from a group of 4,000 children, aged 6 to19. The data was taken from the National Health and Nutrition Survey, a study on the health of children in the United States done each year by the Center for Disease Control and Prevention.

    While looking through the survey results, she noticed that more than half of the kids who took part in the study were dehydrated (脱水的). Of that group, boys were 76% more likely than girls not to have enough water in their system. Nearly one quarter of the kids in the survey reported drinking no plain water at all.

    “These findings highlight (突出) a possible health issue that wasn't given a lot of attention in the past,” Kenney said in a statement. “Even though for most of these kids this is not an immediate and great health risk, this is an issue that could really be reducing quality of life and well-being for many children and youth.”

    The United States-National Agriculture Library says average kids need between 10 to 14 cups of water every day. This water can come from a mix of drinks and foods that contain high amounts of water, such as celery, melons or tomatoes. It is also suggested that fluids (液体) come from water instead of sugary drinks that are high in calories and can lead to weight problems.