单项选择题
A.大于0.3m; B.大于0.5m; C.大于0.7m; D.大于1m
A.0.4 B.0.6 C.0.8
A.1/4至3/4 B.1/3至3/4 C.1/4至2/3 D.1/2至3/4
A.100mm B.150mm C.200mm D.300mm
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