\[\begin {array} {1 1} (a)\;\frac{(a/b)^x}{\log (a/b)}+\frac{(b/a)^x}{\log (b/a)}-2x+c \\ (b)\;\bigg(\frac{a/b}{\log (a/b)}\bigg)^x+\bigg(\frac{b/a}{\log (b/a)}\bigg)^x-2x+c \\ (c)\;\bigg(\frac{a}{b}\bigg)^x+\bigg(\frac{b}{a}\bigg)^x -2x+c \\ (d)\;None \end {array}\]