15. The chemical potential of species i (\( \mu_i \)) is equal to (A)(\( \partial \)G/\( \partial \)ni)T, V, nj (B)(\( \partial \)U/\( \partial \)ni)T, V, nj (C)(\( \partial \)H/\( \partial \)ni)T, V, nj (D)(\( \partial \)A/\( \partial \)ni)T, V, nj (E)none of the above