Three resistors having resistances `` r _{1}, r _{2} `` and `` r _{3} `` are connected as shown in the given circuit. The ratio `` \frac{i_{3}}{i_{1}} `` of currents in terms of resistances used in the circuit is :

(A) `` \frac{ r _{1}}{ r _{2}+ r _{3}} ``
(B) `` \frac{ r _{2}}{ r _{2}+ r _{3}} ``
(C) `` \frac{r_{1}}{r_{1}+r_{2}} ``
(D) `` \frac{ r _{2}}{ r _{1}+ r _{3}} ``