题干

某科学兴趣小组的同学在老师的指导下,正确完成如图所示两个实验。已知所用实验装置气密性良好。

关于该实验,有如下说法:

①红磷熄灭并冷却后才能打开弹簧夹;

②点燃酒精灯加热铜丝,可观察到铜丝由红色变成黑色;

③停止加热后即可读出注射器内气体的体积约为24mL;

④实验取用铜丝质量的多少不会影响实验结果;

⑤两个实验均能证明空气是混合物;

⑥两个实验均能证明空气中约含1/5体积的氧气.

其中正确说法的个数有(  )

A:2个

B:3个

C:4个

D:5个

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答案(点此获取答案解析)

C

同类题4

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.