#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <climits>
#include <cstring>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <vector>
#include <list>
#define rep(i,m,n) for(i=m;i<=n;i++)
#define rsp(it,s) for(set<int>::iterator it=s.begin();it!=s.end();it++)
#define mod 1000000007
#define inf 0x3f3f3f3f
#define vi vector<int>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ll long long
#define pi acos(-1.0)
#define pii pair<int,int>
#define Lson L, mid, rt<<1
#define Rson mid+1, R, rt<<1|1
const int maxn=1e5+10;
using namespace std;
ll gcd(ll p,ll q){return q==0?p:gcd(q,p%q);}
ll qpow(ll p,ll q){ll f=1;while(q){if(q&1)f=f*p;p=p*p;q>>=1;}return f;}
int n,m,k,t,p[maxn],a[maxn],d[maxn],q[maxn],ans;
int find(int x)
{
    return p[x]==x?x:p[x]=find(p[x]);
}
int main()
{
    int i,j;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d%d",&n,&m);
        ans=0;
        memset(d,0,sizeof d);
        memset(q,0,sizeof q);
        rep(i,1,n)scanf("%d",&a[i]),p[i]=i;
        while(m--)
        {
            int b,c;
            scanf("%d%d",&b,&c);
            d[b]++,d[c]++;
            int fa=find(b),fb=find(c);
            if(fa!=fb)p[fa]=fb;
        }
        int cnt=0;
        rep(i,1,n)
        {
            int fa=find(i);
            if(p[fa]!=i&&!q[p[fa]])cnt++,q[p[fa]]=1;
        }
        if(cnt>1){puts("Impossible");continue;}
        else if(cnt==0)
        {
            rep(i,1,n)ans=max(ans,a[i]);
            printf("%d\n",ans);
            continue;
        }
        cnt=0;
        rep(i,1,n)
        {
            if(d[i]&1)cnt++;
            int now=(d[i]+1)/2;
            if(now&1)ans^=a[i];
        }
        if(cnt==2)
        {
            printf("%d\n",ans);
        }
        else if(cnt==0)
        {
            ans=0;
            int ma=0;
            rep(i,1,n)
            {
                int now=(d[i]+1)/2;
                if(now&1)ans^=a[i];
            }
            rep(i,1,n)if(d[i])ma=max(ma,ans^a[i]);
            printf("%d\n",ma);
        }
        else puts("Impossible");
    }
    //system("Pause");
    return 0;
}