29. For any galvanic cell to operate, which of the following statements is true?
(A)△G° and E° must both be positive.
(B)△G° must be negative and E° must be positive.
(C)△G° and E' must both be negative.
(D)△G° must be positive and E° must be negative.
(E)△G° must be zero and E° must be negative.