单项选择题
A.80~60mmB.60~40mmC.100~80mmD.40~20mm
A.400~200mmB.600~200mmC.800~400mmD.400~300mm
A.5~2mmB.20~10mmC.10~5mmD.2~0.5mm
A.不均匀B.太大C.太小D.均匀
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