题干

下列说法正确的有(  )

A:燃料燃烧不充分,它的热值会减小

B:物质的比热容与物质的质量、吸热的多少、升高的温度有关

C:导体的电阻与导体的材料、长度、截面积、温度等有关,与导体中是否有电流没有关系

D:用电器两端的电压发生改变时,额定功率也会随着改变

上一题 下一题 0.0难度 选择题 更新时间:2014-08-13 03:34:50

答案(点此获取答案解析)

C

同类题2

Bobby was sitting out in his back yard in the snow. There were a few holes in his shoes. He thought hard, but he could not come up with an idea for his mother's Christmas gift.
Ever since his father had died three years ago, his mother worked nights at the hospital, but the small money she made could hardly be enough for their needs.
Although the family lacked in money and material things, they got more love in the family. The children ran the family when their mother was absent. All three of Bobby's sisters had already made beautiful gifts for their mother.
It was Christmas Eve already, and he had nothing. Bobby started to walk down to the street. He walked from shop to shop. Everything seemed so beautiful and so far away. It was getting dark. Suddenly he found a shiny dime (一角硬币) on the ground. Never has anyone felt so wealthy as Bobby did at the moment. It was enough to buy a rose with one dime.
He went inside a flower shop. When the owner asked if he could help him, Bobby took out the dime and asked if he could buy one flower. The shop owner looked at Bobby, then said, "You just wait here and I’ll see what I can do for you."
The shop owner returned holding a dozen of red roses in his hand. Bobby's heart sank (下沉) as the owner put them gently into a long white box. "That will be a dime, young man," said the shop owner, reaching out his hand for the dime. Slowly, Bobby moved his hand to give the man his dime.
Then the shopkeeper's wife appeared. "Where are the red roses?"
The shop owner said, "A strange thing happened to me this morning. I thought I heard a voice telling me to leave a dozen of my best roses for a special gift. When I saw that little boy tonight, I knew who that voice was."