#include <iostream>
#include <iomanip>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <queue>
#include <deque>
#include <cmath>
#include <algorithm>
#include <cassert>
#include <chrono>
#include <random>
#include <string>
#include <numeric>
#include <complex>
#include <tuple>
#include <utility>
#include <bitset>
#include <array>
#include <stack>
#include <sstream>

using namespace std;
typedef long long ll;
 
string to_string(string a) { return '"' + a + '"'; }
string to_string(char a) { return "'" + string(1, a) + "'"; }
string to_string(const char* a) { return to_string((string) a); }
string to_string(bool a) { return a ? "true" : "false"; }
template <class T1, class T2>
string to_string(pair<T1, T2> a) {
    return "(" + to_string(a.first) + ", " + to_string(a.second) + ")";
}
template <class T>
string to_string(T a) {
    bool first = true; string res = "{";
    for (const auto& i : a) {
        if (!first) res += ", ";
        first = false;
        res += to_string(i);
    }
    res += "}";
    return res;
}
void debug_out() { cerr << endl; }
template <class T1, class... T2>
void debug_out(T1 a, T2... b) {
    cerr << " " << to_string(a);
    debug_out(b...);
}
 
#ifdef LOCAL
#define out(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define out(...) 42
#endif

clock_t start_time; void start_timer() { start_time = clock(); }
double get_time() { return (double) (clock() - start_time) / CLOCKS_PER_SEC; }

void Solve();

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
#ifdef LOCAL
    freopen("usr/share/man/man1/input.txt", "r", stdin);
#endif
    start_timer();
    Solve();
#ifdef LOCAL
    cerr << fixed << setprecision(3);
    cerr << endl << "Time spent: " << get_time() << endl;
#endif
    return 0;
}

// do something, stay focused
// look for stupid bugs
// guess, slow, stress
// don't overgeneralize
// don't rush

// don't waste time on standings

// SOLVE THE PROBLEM OR DIE TRYING
// THE SOLUTION IS ALWAYS SIMPLE
// THE CODE IS ALWAYS SHORT

const int N = 2e5 + 5;
const int inf = 1e9;

int par[N];
int dep[N];
vector<int> g[N];
bool used[N];
int sz[N];
int msz[N];
vector<int> vis;
int mx;
vector<int> ans;
queue<int> q;
int d[N];

void init(int n) {
    for (int i = 1; i <= n; i++) {
        par[i] = i;
        dep[i] = 0;
        g[i].clear();
        used[i] = 0;
        sz[i] = 0;
        msz[i] = 0;
        d[i] = 0;
    }
    vis.clear();
    ans.clear();
    while (!q.empty()) {
        q.pop();
    }
}

int find(int v) {
    if (v == par[v]) {
        return v;
    }
    return par[v] = find(par[v]);
}

bool unite(int u, int v) {
    u = find(u);
    v = find(v);
    if (u == v) return 0;
    if (dep[u] < dep[v]) swap(u, v);
    par[v] = u;
    if (dep[u] == dep[v]) dep[u]++;
    return 1;
}

void calc_sz(int v, int p = 0) {
    vis.push_back(v);
    sz[v] = 1;
    msz[v] = 0;
    for (int u : g[v]) {
        if (u == p || used[u]) continue;
        calc_sz(u, v);
        sz[v] += sz[u];
        msz[v] = max(msz[v], sz[u]);
    }
}

int dfs_d(int v, int p = 0) {
    int res = d[v];
    for (int u : g[v]) {
        if (u == p || used[u]) continue;
        d[u] = d[v] + 1;
        res = max(res, dfs_d(u, v));
    }
    return res;
}

int get_cen(int v) {
    vis.clear();
    calc_sz(v);
    int min_sz = inf;
    int cen = -1;
    for (int u : vis) {
        int size = max(msz[u], int(vis.size()) - sz[u]);
        if (min_sz > size) {
            min_sz = size;
            cen = u;
        }
    }
    used[cen] = 1;
    return cen;
}


void Solve() {
    int T;
    cin >> T;
    while (T--) {
        int n, m;
        cin >> n >> m;
        init(n);
        for (int i = 1; i <= m; i++) {
            int u, v;
            cin >> u >> v;
            if (unite(u, v)) {
                g[u].push_back(v);
                g[v].push_back(u);
            }
        }
        while ((mx + 1) * (mx + 1) <= n) mx++;
        if (mx * mx < n) mx++;
        q.push(get_cen(1));
        while (!q.empty()) {
            int v = q.front();
            q.pop();
            ans.push_back(v);
            for (int u : g[v]) {
                if (used[u]) continue;
                d[u] = 1;
                if (dfs_d(u, v) <= mx) continue;
                int cen = get_cen(u);
                q.push(cen);
            }
        }
        assert(ans.size() <= mx);
        sort(ans.begin(), ans.end());
        cout << ans.size() << "\n";
        for (int i : ans) {
            cout << i << " ";
        }
        cout << "\n";
    }
}