题干

纯铁的熔点为1535℃,而高炉中炼铁时生铁(含碳量较高的铁的合金)在1200℃左右就熔化了,这是因为(  )

A:铁的纯度越高熔点越低

B:合金的熔点比其成分物质的熔点高

C:因为形成了铁碳合金,所以熔点变低

D:在高炉中熔化的过程中发生了化学反应

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答案(点此获取答案解析)

C

同类题4

根据短文内容,从A、B、C、D四个选项中选出一个能填入相应空格内的最佳答案。

The Bone in Throat

    Once upon a time, there was a lazy wolf living in a forest. Near his house was a pond. Many animals came to 1 to drink water. The wolf was always there in search of food.

    One day, he was sitting near the pond, hoping to get something 2. When suddenly he saw a dead bull, “Aha! What a luck! Now I can eat all I want.” he thought and his 3started watering.

    He began to eat the bull. A thought came into his mind, “if 4 beast comes this way, he will ask for a share. I had better eat 5.” ‘Grub! Grub! Grub!' he chewed, faster and faster. Suddenly, a piece of bone stuck in his throat. “Ohh! Errk!” cried the wolf. He tried to pull it out of his mouth. He tried to cough it out but it didn't 6 . Next, he tried to swallow (吞) it down but he failed.

    “Ooh, the bone in my throat hurts me. What 7 I do now?” thought the wolf. Soon he remembered that a crane (鹤) lived on the nearby river bank.

    The wolf went to the crane and pleased, “My dear Crane! I have got a bone stuck in my throat. I will give you a present 8 you pull it out of my throat.” The crane took pity on the wolf. He asked the wolf to look up 9 his mouth open. The crane then put its head into the wolf's mouth and pulled out the bone. “Oh! What a relief!” the wolf said. “Now where is my present?” asked the crane. “What present?” the wolf replied, pretending not remembering its promise. “You said that you would give me a present if I removed the bone from your throat,” said the crane angrily. “Hah! Isn't it a present that you put your head into my mouth and got out 10? I could have easily broken your head while your head was inside my mouth.”