#include <bits/stdc++.h>
#define MULTI int _; cin >> _; while(_--)
#define fi first
#define se second
#define pb(a) push_back(a)
#define rep(i, n) for(int i = 0; i < n; i++)
#define reps(i, n, m) for(int i = n; i <= m; i++)
#define repsv(i, n, m) for(int i = n; i >= m; i--)
#define vsz(a) (int)(a.size())
#define mp(a, b) make_pair(a, b)
#define all(a) a.begin(), a.end()

using namespace std;

typedef pair<double, double> pdd;
typedef pair<int, int> pii;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef long long int ll;
typedef long double ld;
typedef vector<ll> vll;

#ifdef LOCAL
#include "debugs.hpp"
#else
#define dbg(...) 0
#endif

vector<vi> to;

void rmv(int i, int rn, vb &ex){
    if(rn < 0 || (ex[i] == false)) return;
    rn--;
    ex[i] = false;
    for(int j : to[i])
        rmv(j, rn, ex);
}

void solve(){
    int n, m;
    cin >> n >> m;
    vb ex(n, true);
    to = vector<vi>(n);
    rep(i, m){
        int u, v;
        cin >> u >> v;
        u--, v--;
        to[u].pb(v);
        to[v].pb(u);
    }
    int rn = ceil(sqrt((double)n));
    vi res;
    rep(i, n){
        if(ex[i]){
            rmv(i, rn, ex);
            res.pb(i);
        }
    }
    cout << vsz(res) << '\n';
    for(int i : res)
        cout << i+1 << ' ';
    cout << '\n';
}

int main(){
    ios_base::sync_with_stdio(false);
    MULTI
    solve();
}