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问题
单项选择题
当活塞销选用20钢制作时，应进行的热处理是（）
A．淬火
B．淬火+低温回火
C．渗碳+淬火+低温回火
D．渗碳+正火
答案
参考答案：C
选择题
I _____ my son _____ a doctor, but he wasn’t good enough at science.
A．hoped; became
B．hoped; could become
C．had hoped; would become
D．had hoped; would have become
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名词解释
城市化经济
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