单项选择题
A.1.2或1.6mm B.1.6或1.8mm C.1.8或2.0mm D.2.0mm以上
A.8mm B.12mm C.15mm D.20mm
A.40% B.50% C.60% D.70%
A.三倍 B.四倍 C.五倍 D.六倍
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