下列说法正确的是（） A．手持量筒量取一定体积的液体 B_爱下问搜题

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问题选择题

下列说法正确的是（　　）

A．手持量筒量取一定体积的液体

B．用托盘天平称量5.65g食盐

C．铁、氮气、氯化钠分别是由分子、原子、离子构成的

D．生铁和钢的物理性质不同主要是因为含碳量不同

答案

A、用量筒量取一定体积的液体时，量筒必须放平，手持量筒不容易放平，故A错误；

B、托盘天平的准确度是0.1g，不能称取5.65g食盐，故B错误；

C、铁是由铁原子构成的，氮气是由氮分子构成的，氯化钠是由离子构成的，故C错误；

D、由于生铁和钢的含碳量不同，决定了生铁和钢的物理性质不同，故D正确．

故选D．

完形填空

阅读下面短文.从短文后各题所给的四个选项A、B. C和D中,选出可以填入空白处的最佳选项，并在答题卡上将该项小涂黑。
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However, he opened the shop’s door and went inside. Standing        and straight, he told the shopkeeper what he wanted and asked him to        it for some time. The shopkeeper      .
Reuben walked out into the sunlight and thought he would        the five dollars and not tell anybody. Hearing the sound of hammering (敲打), he had a (n)       . People built their own homes using nails (钉子) and       nail bags outside. He could sell them back to the nail factory for five cents a piece. That day he sold two bags and hid the       .
It was evening when Reuben got home. Dora was at the kitchen, ready to serve        as Reuben sat at the table. He looked at his        and smiled.
Every day after school, Reuben        the town, collecting nail bags. On the day the school closed for the summer holiday, Reuben was happier than anyone        he would have more time for his       . Finally, the time had come! He        the coins. It was five dollars in all. Then he headed for the shop. “I have the money,” he       told the owner. And he got his     .
Racing home, Reuben       as he ran to his mother, “Here, Mum! Here!” He      a small box in her big hand. She        it carefully and saw the golden word “Mother” inside the box. It was Mother’s Day. Dora had never received such a       . She smiled happily and held her son in her arms.

多选题

如图所示，理想变压器原副线圈匝数之比为4：1，原线圈接入一电压为u=220_{sin100πtV的交流电源，副线圈接一个R=27.5Ω的负载电阻．则下述结论正确的是（　　）}

A．副线圈中电压表的读数为55V

B．副线圈中输出交流电的周期为0.01s

C．原线圈中电流表的读数为0.5A

D．原线圈中的输入功率为110W