单项选择题
A.小于3% B.小于5% C.5%～10% D.大于10%
A.小于0.25% B.0.25％～0.6% C.0.4% D.0.6%
A.+2 B.+3 C.+4 D.+5
A.铜 B.铝 C.铁 D.锌
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