#include <bits/stdc++.h>

using std::cin;
using std::cout;
using std::endl;
using std::vector;
using std::string;
using ll = long long;
using vi = vector<ll>;
using vii = vector<vi>;
using pii = std::pair<ll,ll>;

#define ln "\n"
#define pb emplace_back
#define mp std::make_pair
#define mtp std::make_tuple
#define rep(i,j,k) for(ll i=ll(j); i<ll(k); i++)
#define REP(i,j,k) for(ll i=ll(j); i<=ll(k); i++)
#define per(i,j,k) for(ll i=ll(j); i>=ll(k); i--)
#define all(a) a.begin(),a.end()

constexpr ll inf = (1ll<<60);
constexpr ll mod = 1e9+7;
constexpr ll mul = 23;

void dec(std::map<ll,ll> &mem, ll el){
    mem[el]--;
    if(mem[el] == 0) mem.erase(el);
}

void solve(){
    ll N; cin >> N;
    constexpr ll maxi = 11;
    vi cnt(maxi);
    vi A(N);
    rep(i,0,N) cin >> A[i];
    rep(i,0,N) cnt[A[i]]++;
    vi mul(maxi+1,1);
    rep(i,0,maxi) mul[i+1] = mul[i]*4;
    ll M = mul[maxi];
    vi dp(M,-1);
    vi a, b;
    std::function<bool(ll)> dfs = [&](ll now){
        if(dp[now] != -1) return bool(dp[now]);
        vi v(maxi);
        ll nvv = now;
        rep(i,0,maxi){
            v[i] = nvv%4;
            nvv /= 4;
        }
        ll total = 0;
        rep(i,0,maxi){
            total += v[i];
        }
        dp[now] = 1;
        if(total == 1) return true;
        rep(i,0,maxi){
            if(v[i] >= 2){
                bool flag = dfs(now-mul[i]);
                if(flag){
                    a.pb(i);
                    b.pb(i);
                    dp[now] = 1;
                    return true;
                }
            }
            rep(j,i+1,maxi){
                if(v[i] == 0 || v[j] == 0) continue;
                if((i+j)%2) continue;
                ll k = (i+j)/2;
                if(v[k] == 3) continue;
                bool flag = dfs(now-mul[i]-mul[j]+mul[k]);
                if(flag){
                    a.pb(i);
                    b.pb(j);
                    dp[now] = 1;
                    return true;
                }
            }
        }
        dp[now] = 0;
        return false;
    };
    ll nval = 0;
    rep(i,0,maxi){
        nval += std::min(3ll, cnt[i])*mul[i];
    }
    if(dfs(nval)){
        rep(i,0,maxi){
            rep(j,3,cnt[i]){
                a.pb(i);
                b.pb(i);
            }
        }
        reverse(all(a));
        reverse(all(b));
        assert(a.size() == N-1);
        rep(i,0,N-1) cout << a[i] << " " << b[i] << ln;
    }
    else cout << -1 << ln;
}

int main(){
    cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    ll T; cin >> T;
    while(T--){
        solve();
    }
}