单项选择题
A.20mm B.30mm C.40mm D.50mm
A.1±0.5mm B.1±1.5mm C.2±0.5mm D.2±1.5mm
A.2kPa B.3kPa C.4kPa D.5kPa
A.56mm B.57mm C.58mm D.59mm
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