#include<bits/stdc++.h>
#include <vector>

#define range(x) begin(x), end(x)

using namespace std;


int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;
    cin >> t;
    while (t--) {
        int n, m;
        cin >> n >> m;
        vector<vector<int>> G(n + 1);
        vector<int> fa(n + 1);
        vector<int> deg(n + 1, 0);
        for (int i = 1; i <= n; i++) {
            fa[i] = i;
        }
        auto find = [&](int u) {
            while (u != fa[u]) u = fa[u] = fa[fa[u]];
            return u;
        };

        for (int i = 0; i < m; i++) {
            int u, v;
            cin >> u >> v;
            if (find(u) != find(v)) {
                fa[find(u)] = find(v);
                G[u].push_back(v);
                G[v].push_back(u);
                deg[u]++, deg[v]++;
            }
        }
        vector<int> dp(n + 1, 1);
        queue<int> q;
        for (int i = 1; i <= n; i++) {
            if (deg[i] == 1) {
                q.push(i);
            }
        }
        vector<int> ans;
        int lim = ceil(sqrt(n));
        while (lim * lim < n)lim++;
        while ((lim - 1) * (lim - 1) >= n) lim--;
        while (!q.empty()) {
            int u = q.front();
            q.pop();
            if (deg[u] == 0 || dp[u] >= lim) {
                ans.push_back(u);
                dp[u] = 0;
            }
            for (int v: G[u]) {
                deg[v]--;
                dp[v] += dp[u];
                if (deg[v] == 1) {
                    q.push(v);
                }
            }
        }

        cout << ans.size() << "\n";
        for(int u:ans){
            cout << u <<" ";
        }
        cout << "\n";


    }


    return 0;
}