单项选择题
A.0.2mm B.0.3mm C.0.5mm D.0.6mm
A.1/2 B.1/3 C.1/10 D.1/6
A.2cm2 B.3cm2 C.4cm2 D.5cm2
A.10MPa B.15MPa C.20MPa D.35MPa
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