what would be the expression in place of ? in the Van't Hoff equation: $ log \frac{K_2}{K_1} = \frac {\Delta H^\circ}{2.303R} [?]$

Question

(a) $ \frac {1}{T_1} + \frac {1}{T_2} $

(b) $ \frac {1}{T_1} - \frac {1}{T_2} $

(c) $ \frac {1}{T_2} - \frac {1}{T_1} $

(d) $ \frac {1}{T_1 T_2} $