In complete graph,
for vertex V1= n-1 ways to traverse
for vertex V2= n-2 ways to traverse
for vertex V3= n-3 ways to traverse
.
.
.
.
.
for vertex Vn= 1 way only
Hence total ways= (n-1)(n-2)(n-3)….2.1 = (n-1)!
also every path is considered twice hence (n-1)! /2
Hence option D