#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int MAXN = 100000+5;
int a[MAXN];
int degree[MAXN];
int n, m;

void solve()
{
    memset(degree, 0, sizeof(degree));
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; ++i)
        scanf("%d", &a[i]);
    int u, v;
    while(m--){
        scanf("%d%d", &u, &v);
        ++degree[u];
        ++degree[v];
    }
    int odd_sum = 0;
    for(int i = 1; i <= n; ++i){
        if(degree[i]&1)
            ++odd_sum;
    }
    if(!(odd_sum == 0 || odd_sum == 2)){
        printf("Impossible\n");
        return;
    }
    int val = 0;
    for(int i = 1; i <= n; ++i){
        if((degree[i]/2)&1)
            val ^= a[i];
    }
    if(odd_sum == 0){
        int res = 0xffffffff;
        for(int i = 1; i <= n; ++i){
            if(degree[i] != 0)
                res = max(res, val^a[i]);
        }
        printf("%d\n", res);
    }
    else{
        int s = 0, e = 0;
        for(int i = 1; i <= n; ++i){
            if(degree[i]&1){
                if(s == 0){
                    s = i;
                }
                else{
                    e = i;
                    break;
                }
            }
        }
        int res = val^a[s]^a[e];
        printf("%d\n", res);
    }
}

int main()
{
    int t;
    scanf("%d", &t);
    while(t--){
        solve();
    }
    return 0;
}