单项选择题
A.≥1/2 B.≥1/4 C.≥1/5 D.≥1/3
A.3天 B.7天 C.14天 D.28天
A.15~20mm B.20~30mm C.10~20mm D.15~25mm
A.400mm B.500mm C.300mm D.600mm
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