单项选择题
A.凹处没有镀层或镀层发花B.镀层粗糙、色灰、光亮度差C.镀层氢脆D.镀层有明显裂纹
A.HCrO4-B.(Cr2O7)2-C.Cr6+D.Cr3+
A.50:1B.100:1C.150:15D.200:1