单项选择题
A.0.2mm B.0.3mm C.0.25mm D.不允许
A.5∶1 B.3∶1 C.2∶1 D.1∶1
A.2/3~3/4 B.1/2~2/3 C.1/3~3/8
A. 2/3~3/4 B.1/2~2/3 C.1/3~3/8
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