CEMC Gauss (Grade 8), 2000

The homes of Fred ($F$), Sandy ($S$), Robert ($R$), and Guy ($G$) are marked on the rectangular grid with straight lines joining them. Fred is considering four routes to visit each of his friends: (i) $F \to R \to S \to G$ (ii) $F \to S \to G \to R$ (iii) $F \to R \to G \to S$ (iv) $F \to S \to R \to G$. If $FS = 5$ km, $SG = 9$ km and $SR = 12$ km, the difference between the longest and the shortest trip (in km) is

(A) $8$ (B) $13$ (C) $15$ (D) $2$ (E) $0$