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问题 单项选择题

按EN12021标准，呼吸用压缩空气质量油含量，最大0.5mg/m3，测试流量（）L/min，测量时间为30分钟。

A.0.3L/min

B.2L/min

C.1L/min

D.3L/min

答案

参考答案：B

单项选择题

Dick was born in a poor family. His father had a small boat and went fishing in the morning and sold the fish in the market in the afternoon. Then he bought some food for his family. When winter came, they were often hungry. One morning the hungry man fell into the river and wasn’t found. Dick’s mother left her three-year-old son without saying good-bye. His aunt had to look after him.
Twenty years passed. Dick became a tall, p man. He found work on a farm. He worked hard and wanted to get more money. He often went to see his aunt with some nice presents. The woman was very happy but one day she died in a traffic accident. The young man was very sad. After he buried her, he decided to buy a beautiful tombstone(墓碑)for her. He went to town and came in a shop, but all the tombstones were too expensive. He asked, "Do you sell an old tombstone, sir" "Yes, we do, sir," answered the shopkeeper. "Is it as expensive as the new one"
"No, it’s much cheaper," said the man. "But another name was engraved (刻) on it." "It doesn’t matter," said Dick. "My aunt couldn’t read.\

If ______, the family members were hungry.

A．Dick’s father could catch no fish in winter

B．Dick’s father had a boat in winter

C．Dick’s father had to look after him in winter

D．no food was sold in winter
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多选题
如图所示，理想变压器的原副线圈匝数比n1：n2=1：10，副线圈与阻值R=20Ω的电阻相连．原线圈两端所加的电压u=20sin20πt(V)，则（　　）

A．副线圈输出交流电的频率为10Hz

B．交流电压表的示数为20V

C．电阻R上消耗的电功率为2kW

D．原线圈中电流的最大值为100A
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