单项选择题
A.2:7:1B.2:6:2C.3:6:1D.4:5:1
A.2~5cmB.5~10cmC.10~15cmD.大于15cm
A.5~6B.6~7C.7~9D.9~11
A.4~5B.4~6C.3~4D.3~5
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