28. For any operating concentration cell, which of the following statements is true?
(A)E and E°must both be positive.
(B)E must be zero and E°must be positive
(C)E° must be zero and E must be positive.
(D)E and E° must both be negative.
(E)E° must be positive and E must be negative.

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統計： A(1), B(1), C(0), D(0), E(0) #2788676