#include <bits/stdc++.h>

#define IO	       { ios_base::sync_with_stdio(false); cin.tie(0); }

using namespace std;


int n, m;
vector<vector<int>> adj;
vector<int> vis;

int lim;

void dfs(int node, int sz) {
    vis[node] = 1;
    if (sz == lim) return ;
    for (int v: adj[node]) {
        if (!vis[v]) {
            dfs(v, sz + 1);
        }
    }
}

void solve() {
    cin >> n >> m;
    for (int i=1; ;i++) {
        if (i*i >= n) {
            lim = i;
            break;
        }
    }
    
    adj.clear();
    vis.assign(n+100, 0);
    adj.resize(n+100);
   

	for (int i = 0; i < m; i++) {
		int a, b;
		cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
	}
    
    vector<int> ans;
    for (int i=1; i<=n; i++) {
        if (!vis[i]) {
            ans.push_back(i);
            dfs(i, 0);
        }
    }

    cout << ans.size() << endl;
    for (int v: ans) cout << v << " ";
    cout << endl;

}

int main() {
    IO;
    int t;
    cin >> t;
    while(t--) {
        solve();
    }
}