1 #include<stdio.h>
  2 #include<algorithm>
  3 #include<string.h>
  4 #include<iostream>
  5 #include<queue>
  6 #include<stdlib.h>
  7 #include<math.h>
  8 #include<set>
  9 using namespace std;
 10 int bin[100005];
 11 int cnt[100005];
 12 int du[100005];
 13 int ans[100005];
 14 set<int>que;
 15 int main(void)
 16 {
 17     int n;
 18     scanf("%d",&n);
 19     while(n--)
 20     {
 21         que.clear();
 22         int i,j;
 23         memset(cnt,0,sizeof(cnt));
 24         for(i = 0; i <= 100005; i++)
 25         {
 26             bin[i] = i;
 27             du[i] = 1;
 28         }
 29         int N,M;
 30         scanf("%d %d",&N,&M);
 31         if(M==0)printf("0\n");
 32         else
 33         {
 34             for(i = 1; i <= N; i++)
 35             {
 36                 scanf("%d",&ans[i]);
 37             }
 38             while(M--)
 39             {
 40                 int x,y;
 41                 scanf("%d %d",&x,&y);
 42                 cnt[x]++;
 43                 cnt[y]++;
 44                 int xx,yy;
 45                 for(xx = x; bin[xx]!=xx;)
 46                     xx = bin[xx];
 47                 for(yy = y; bin[yy]!=yy;)
 48                     yy = bin[yy];
 49                 if(xx != yy)
 50                 {
 51                     if(du[xx]>du[yy])
 52                     {
 53                         bin[yy] = xx;
 54                         du[xx] += du[yy];
 55                     }
 56                     else
 57                     {
 58                         bin[xx] = yy;
 59                         du[yy] += du[xx];
 60                     }
 61                 }
 62             }
 63             for(i = 1; i <= N; i++)
 64             {
 65                 if(cnt[i])
 66                 {
 67                     int xx;
 68                     for(xx = i; xx!=bin[xx];)
 69                         xx = bin[xx];
 70                     que.insert(xx);
 71                 }
 72             }
 73             int cn = 0;
 74             for(i = 1; i <= N; i++)
 75             {
 76                 if(cnt[i])
 77                 {
 78                     if(cnt[i]%2)
 79                     {
 80                         cn++;
 81                     }
 82                 }
 83             }
 84             int sum = 0;
 85             if(cn == 1|| cn > 3||que.size()!=1)
 86             {
 87                 //printf("1\n");
 88                 printf("Impossible\n");
 89             }
 90             else if(cn == 2)
 91             {
 92                 for(i = 1; i <= N; i++)
 93                 {
 94                     if(cnt[i]>1)
 95                         cnt[i]=cnt[i]+1;
 96                     cnt[i]/=2;
 97                     if(cnt[i]%2)
 98                         sum^=ans[i];
 99                 }
100                 printf("%d\n",sum);
101             }
102             else
103             {
104                 for(i = 1; i <= N; i++)
105                 {
106                     if(cnt[i])
107                     {
108                         sum ^= ans[i];
109                     }
110                 }
111                 int flag = 0;
112                 int k = sum;
113                 for(i = 1; i <= N; i++)
114                 {
115                     if(cnt[i])
116                     {
117                         if(!flag)
118                             sum^=ans[i],flag = 1;
119                         else sum = max(sum,k^ans[i]);
120                     }
121                 }
122                 printf("%d\n",sum);
123             }
124         }
125     }
126     return 0;
127 }