#include<cstring>

 #include<algorithm>

 #include<queue>

 #include<vector>

 #include<set>

 #define CLR(a,b) memset((a),(b),sizeof((a)))

 using namespace std;

 const int N = ;

 const int inf = 0x3f3f3f3f;

 int n, m;

 int a[N];

 int du[N];

 int main(){

     int t, i, j, b, c, f, ans, dd, ma;

     scanf("%d", &t);

     while(t--){

         ans = ;

         scanf("%d %d", &n, &m);

         f = ;

         ma = ;

         CLR(du, );

         for(i = ; i<= n; ++i)

             scanf("%d", &a[i]);

         for(i = ; i <= m; ++i){

             scanf("%d %d", &b, &c);

             du[b]++; du[c]++;

         }

         dd = ;

         for(i = ; i <= n; ++i){

             if(du[i]%) dd++;

         }

         if(dd ==  || dd==) f = ; // 欧拉路的奇度顶点数为 2 或 0

         if(!f){printf("Impossible\n");continue;}

         for(i = ; i<= n; ++i){

             if(((du[i] + )/) % == )

                 ans ^= a[i];

         }

         if(!dd){//欧拉回路时枚举起点

             for(i = ; i <= n; ++i){

                 int t = ans ^a[i];

                 ma= max(ma, t);

             }

             ans = ma;

         }

         printf("%d\n", ans);

     }

     return ;

 }