题干

滥用抗生素会使细菌出现耐药性,长此以往,应对细菌感染,人类将无药可用.下列有关说法正确的是(    )

A:抗生素的使用可增强人体的免疫力,但会引起细菌的定向变异

B:群落是生物进化的基本单位,突变可为进化提供原材料

C:“耐药性”基因频率的改变导致病菌发生了进化

D:抗生素的滥用导致“耐药性”细菌被优选出来,是细菌对抗生素进行选择的结果

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答案(点此获取答案解析)

C

同类题5

阅读下面的短文并用英语回答问题,并将答案写在答题卷上标有题号的横线上。

(an extract from Stuart Little)

    When Mrs. Frederick C. Little's second son arrived, everybody noticed that he was not much bigger than a mouse. The truth of the matter was, the baby looked very much like a mouse in every way. He was only about two inches high; and he had a mouse's sharp nose, a mouse's tail, a mouse's whiskers(胡须),and the pleasant, shy manner of a mouse. Before he was many days old he was not only looking like a mouse but acting like one, too-wearing a gray hat and carrying a small cane(手杖).Mr. and Mrs. Little named him Stuart, and Mr. Little made him a tiny bed.

    Unlike most babies, Stuart could walk as soon as he was born. Mrs. Little saw right that the baby clothes she had provided were unsuitable, and she set to work and made him a fine little blue suit. Every morning, before Stuart dressed. Mrs. Little went into his room and weighed him on a small scale(称)which was really used for weighing letters. At birth Stuart could have been sent by first class mail, but his parents preferred to keep him rather than send him away. At the age of a month, he had gained only a third of an ounce(盎司), his mother was so worried that she sent for the doctor.

    The doctor was happy with Stuart and said that it was very unusual for an American family to have a mouse. He took Stuart's temperature and found that it was 98.6, which is normal for a mouse. Everything seemed to be all right, and Mrs. Little was pleased to get such a good report.

    "Feed him up!" said the doctor cheerfully, as he left.

    The home of the Little family was a pleasant place near a park in New York City. In the mornings, the Littles were up early as a general rule. Stuart was a great help to his parents, and to his old brother, because of his small size and because he could do things that a mouse can do and was willing to do them.