问题
单项选择题
X线管阳极靶面所用的物质必须具有（）
A.低原子序数，高熔点
B.低原子序数，低熔点
C.高原子序数，高熔点
D.高原子序数，低熔点
E.低密度、高比重
答案
参考答案：C
解析：靶面材料应具备以下条件：原子序数高、X线发生效率高、熔点高、金属蒸发率低、导电率高以及热传导率高。
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X线管阳极靶面所用的物质必须具有（）
A.低原子序数，高熔点
B.低原子序数，低熔点
C.高原子序数，高熔点
D.高原子序数，低熔点
E.低密度、高比重
参考答案：C
解析：靶面材料应具备以下条件：原子序数高、X线发生效率高、熔点高、金属蒸发率低、导电率高以及热传导率高。
| 补全对话。 | |
B: I've just been to the Three Gorges (三峡). A: Really? 2 B: Right. As you know, we've built a great dam (坝) across the Changjiang river. A: 3 B: Yes, the dam is stopping water these days. And the water is rising 2 meters every day until it is 135 meters high. A: Oh, no wonder (难怪) it's said that the beautiful scenery of Kuimen will be under water. What a pity! B: 4 It has copied in another place with some other places of interest. A: Great! I want to go to the Three Gorges this summer. Would you like to go there with me again? B: I'd love to! 5 1. _________ 2. __________ 3. ___________ 4. ___________ 5. ___________ |