22.水中總餘氯為 4.5mg/L as Cl2,結合餘氯為 2.5 mg/L as Cl2,請問自由餘氯應為何(mg/L as Cl2)?
(A) 2
(B) 3
(C) 5
(D) 7
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統計: A(71), B(7), C(3), D(2), E(0) #1967582
統計: A(71), B(7), C(3), D(2), E(0) #1967582