题干

下列对生命现象及其生物学意义的表述正确的是(    )

A:主动运输使膜内外物质浓度趋于一致

B:细胞凋亡有利于生物体内部环境的稳定

C:精确的模板可保证DNA复制不出现任何差错

D:患伴X显性遗传病的女性后代均为患者

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答案(点此获取答案解析)

B

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完成短文

    Once my mother told me a story. In Africa, when an antelope (羚羊) wakes up every morning, the first thing it thinks about is, “I must be able to run faster than the fastest lion, or I will be k____.” At the same time, a lion wakes from his dream. The first thing the lion thinks about is, “I must be able to catch the ____antelope, or I will die of hunger .” So almost at the same time, the antelope and the lion get up and start running toward the rising sun.

This is life: full of chances and challenges. Whether you are an antelope or a lion, you must go a____when the sun rises. For students, it is just the same. If we don't study hard, sooner or later, we will fall b____the other students. At first, I didn't know what the word “exam” meant. Later, I knew an exam was a kind of competition. In competitions, there are always w____ and losers. As I grew up, I got to know “competition”. In one's life, there must be competitions, so people can improve.

    Each time I saw children playing games and heard their laughter, I wished I were that age again. However, I remembered my parents' words: “You must work very hard in order to have a good f____. ” So I picked up my pen and began to study hard again.

    I was still not sure what competition really meant. One day, I was taking part in an English-speaking competition. When I went to the stage, I saw other students looking at me kindly. I s____ knew what competition was. It is not as cruel as my teacher and parents told me. In fact, competition is the opposite: it is kind and necessary.

    I learned a lot from realizing this . Now I understand better about the world. Competition is important for us all.