#pragma comment(linker, "/STACK:102400000,102400000")

#include <math.h>

#include <time.h>

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include <set>

#include <map>

#include <string>

#include <stack>

#include <queue>

#include <vector>

#include <bitset>

#include <iostream>

#include <algorithm>

#define pb push_back

#define fi first

#define se second

#define icc(x) (1<<(x))

#define lcc(x) (1ll<<(x))

#define lowbit(x) (x&-x)

#define debug(x) cout<<#x<<"="<<x<<endl

#define rep(i,s,t) for(int i=s;i<t;++i)

#define per(i,s,t) for(int i=t-1;i>=s;--i)

#define mset(g, x) memset(g, x, sizeof(g))

using namespace std;

typedef long long ll;

typedef unsigned long long ull;

typedef unsigned int ui;

typedef double db;

typedef pair<int,int> pii;

typedef pair<ll,ll> pll;

typedef vector<int> veci;

const int mod=(int)1e9+7,inf=0x3fffffff,rx[]={-1,0,1,0},ry[]={0,1,0,-1};

const ll INF=1ll<<60;

const db pi=acos(-1),eps=1e-8;

template<class T> void rd(T &res){

    res = 0; int ch,sign=0;

    while( (ch=getchar())!='-' && !(ch>='0'&&ch<='9'));

    if(ch == '-') sign = 1; else res = ch-'0';

    while((ch=getchar())>='0'&&ch<='9') res = (res<<3)+(res<<1)+ch-'0';

    res = sign?-res:res;

}

template<class T>void rec_pt(T x){

    if(!x)return;

    rec_pt(x/10);

    putchar(x%10^48);

}

template<class T>void pt(T x){

    if(x<0) putchar('-'),x=-x;

    if(!x)putchar('0');

    else rec_pt(x);

}

template<class T>inline void ptn(T x){ pt(x),putchar('\n'); }

template<class T>inline void Max(T &a,T b){ if(b>a)a=b; }

template<class T>inline void Min(T &a,T b){ if(b<a)a=b; }

template<class T>inline T mgcd(T b,T d){ return b?mgcd(d%b,b):d; }//gcd模板，传入的参数必须是用一类型

//-------------------------------主代码--------------------------------------//

int g[100100];

int d[100100];

int markpath[100100];

int mark[100100];

struct node{

    int to,next;

}edge[1000100];

int cnt,pre[100100];

void add_edge(int u,int v){

    edge[cnt].to = v;

    edge[cnt].next = pre[u];

    pre[u] = cnt++;

}

void dfs(int s){

    mark[s] = 1;

    for(int p=pre[s];p!=-1;p=edge[p].next){

        int v = edge[p].to;

        if(mark[v] == 1) continue;

        dfs(v);

    }

}

int main()

{

    int T;

    rd(T);

    while (T--) {

        cnt = 0;

        mset(d, 0); mset(markpath, 0); mset(pre, -1); mset(mark, 0);

        int n,m;

        rd(n),rd(m);

        for(int i=1;i<=n;i++)

        {

            rd(g[i]);

        }

        rep(i, 0, m){

            int x,y;

            rd(x),rd(y);

            markpath[x] = 1; markpath[y] = 1;

            add_edge(x,y);

            add_edge(y,x);

            d[x]++; d[y]++;

        }

        int cnt = 0;

        for(int i=1;i<=n;i++){

            if(d[i]%2 != 0) cnt++;

        }

        if(cnt!=0 && cnt!=2){

            printf("Impossible\n");

            continue;

        }

        int flag = 0;

        for(int i=1;i<=n;i++){

            if(markpath[i]==1 && mark[i] ==0){

                flag ++;

                dfs(i);

            }

        }

        if(flag > 1) {

            printf("Impossible\n");

            continue;

        }

        int ans = 0;

        if(cnt == 0){

            int sum = 0;

            for(int i=1;i<=n;i++){

                if( (d[i]/2)%2!=0 )

                {

                    sum ^= g[i];

                }

            }

            for(int i=1;i<=n;i++){

                if(markpath[i]==1)

                    ans = max(ans,sum^g[i]);

            }

        }else{

            int sum = 0;

            for(int i=1;i<=n;i++){

                if(d[i]%2!=0){

                    d[i]++;

                }

                if( (d[i]/2)%2!=0 )

                {

                    sum ^= g[i];

                }

            }

            ans = sum;

        }

        ptn(ans);

    }

    return 0;

}