金属的结晶过程可分为两个阶段：_________和__________。
给你两根相同直径和长度的丝材。一根是锻造的，另一根是铸造的。哪一根的伸长率大？
A grain is()
A. always the same size in all alloys
B. a single crystal ofmetal as seen in the metal"s microstructure
C. can be removed from metals by treating them with methyl methacrylate
D. used to be called a"polytip"
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