单项选择题
A.5% B.20% C.30% D.15%
A.＜1.2‰ B.＜1.5‰ C.＜2‰ D.＜3‰
A.3mm B.4mm C.6mm D.8mm
A.2－4mm B.4－6mm C.6－8mm D.7-9mm
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