0.050μg/ml的Co标准溶液，用石墨炉原子化器的原子吸收分光光度计，每次以5μl与去离子水交替连续

A.准确移取500μg/mL的PO43-贮备液20mL于500mL容量瓶中，用纯水稀释至刻度

B.准确移取500μg/mL的PO43-贮备液10mL于500mL容量瓶中，用纯水稀释至刻度

C.准确移取500μg/mL的PO43-贮备液20mL于100mL容量瓶中，用纯水稀释至刻度

D.准确移取500μg/mL的PO43-贮备液10mL于100mL容量瓶中，用纯水稀释至刻度

A.0.1mg/mL

B.1.0mg/mL

C.0.01mg/mL

D.1.0mg/L

A.25.0mL

B.25.00mL

C.(25.00±0.01)mL

D.(25.00±0.02)mL

A.400CFU/ml或400CFU/g

B.500CFU/ml或500CFU/g

C.500CFU/ml或600CFU/g

D.700CFU/ml或700CFU/g

A.细菌数≤1000个/g或ml

B.细菌数＜500个或ml

C.细菌数≤100个/g或ml

D.细菌数≤10个/g或ml

E.细菌数≤1个/g或ml

A 25. 00 mL sample of unknown Fe³⁺and Cu²⁺required 16. 06 mL of 0. 050 83 mol·L^-1EDTA for complete titrated. A 50. 00 mL sample of unknown was treated with NH₄F to protect the Fe³⁺. Then the Cu²⁺was reduced and masked by addition of thiourea. Upon addition of 25. 00 mL of 0.050 83 mol·L^-1EDTA, the Fe³⁺was liberated from its fluoride complex and formed an EDTA complex The excess EDTA required 19.77 ml of 0. 01883

mol·L^-1Pb²⁺to reach an endpoint using xylenol orange. Find the concentration of Cu²⁺in the unknown.