问题
单项选择题 A1/A2型题
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奈件：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奈件：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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| Last night, when I was driving back home, I noticed a hitchhiker (搭便车的人) who was having no luck getting a ride. I rolled down my 1 and signed to the man to my car. I asked him where he was 2 and he told me he needed a 3 to his doctor's office which would close in 15 minutes. I told him to 4 and he gratefully did so. 5 he got in he told me that he was a 6 and went out to sea for weeks at a time. He took medicine for his nerves and 7 to get another prescription (处方) before he left on the boat. He said that he had prayed (祈 祷) 8 would stop for him so he could be there before the 9 office closed. With some 10 driving we managed to make it there in about 10 11 . I then asked him how he 12 on getting back home and he said he could walk. "I'll patiently 13 for you and bring you back," I told him. He 14 me and said he should only be about 15 minutes. Afterwards he got back in my 15 and tried his hardest to pay me back: offering me dinner, gas money, even offering to ship me 40 lbs of scallops (海扇贝)! I 16 refused, gave him a smile card and asked him to help someone else the next time he had a 17 . I drove him back to where I had picked him up and 18 one more "thank you" he was on his way. I feel that the universe 19 provides us with what we need. In the man's 20 it was a ride, in mine the opportunity to help someone else. | ||||
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