单项选择题
A.20% B.25% C.30% D.35%
A.±5.0 B.±6.0 C.±7.0 D.±3.0
A.60% B.75% C.50% D.85%
A.单螺母;1扣 B.双螺母;2扣 C.双螺母;1扣
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