下列哪种物质测定对水纯度要求最高（）

A.酶活性

B.氧化还原比色法测葡萄糖

C.苦味酸法测肌酐

D.球蛋白

E.白蛋白

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A．If, which

B．So long as, what

C．In case, where

D．Even if, as