#include <bits/stdc++.h>

using namespace std;

void solve() {
    int n, m;
    cin >> n >> m;
    vector<vector<int>> g(n);
    for (int i = 0; i < m; ++i) {
        int u, v;
        cin >> u >> v;
        --u, --v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    int r = 0;
    while (r * r < n)++r;

    vector<char> used(n, 0);
    vector<int> res;
    auto dfs = [&](int v, auto &&dfs) -> int {
        used[v] = 1;
        int mx = 0, dist = -1;
        for (auto to: g[v]) {
            if (used[to])continue;
            int it = dfs(to, dfs);
            dist = max(dist, it + mx);
            mx = max(mx, it);
        }
        if (dist >= r) {
            res.push_back(v);
            return 0;
        }
        return mx + 1;
    };
    dfs(0, dfs);
    if (res.empty())res.push_back(0);
    cout << res.size() << "\n";
    for (auto x: res)cout << x + 1 << " ";
    cout << "\n";
}

int main() {
    cin.tie(0)->sync_with_stdio(false);
    int t;
    cin >> t;
    while (t--)solve();
}