单项选择题
A.1 B.2 C.3 D.4
A.大于150mm B.小于150mm C.小于或等于150mm D.等于150mm
A.10m/s B.15m/s C.20m/s D.30m/s
A.2~3mm B.3~5mm C.5~7mm D.7~9mm
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