//Make CSP great again
//Vengeance
#include <bits/stdc++.h>
#define TASK "TESTCODE"
using namespace std;
const int N = 2e5;
int n, m, sz, depth[N + 1];
vector<int> adj[N + 1], res;
bool visited[N + 1];
void read()
{
    cin >> n >> m;
    for (int i = 1; i <= n; ++ i)
    {
        adj[i].clear();
        visited[i] = false;
    }
    for (int i = 1; i <= m; ++ i)
    {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    res.clear();
    sz = sqrt(n);
}
void DFS(int u)
{
    if (depth[u] % sz == 0)
    {
        res.push_back(u);
    }
    visited[u] = true;
    for (int v : adj[u])
    {
        if (!visited[v])
        {
            depth[v] = depth[u] + 1;
            DFS(v);
        }
    }
}
void solve()
{
    DFS(1);
    cout << res.size() << '\n';
    for (int u : res)
    {
        cout << u << ' ';
    }
    cout << '\n';
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (fopen(TASK".INP", "r"))
    {
        freopen(TASK".INP", "r", stdin);
        //freopen(TASK".OUT", "w", stdout);
    }
    int t = 1;
    bool typetest = true;
    if (typetest)
    {
        cin >> t;
    }
    for (int __ = 1; __ <= t; ++ __)
    {
        //cout << "Case " << __ << ": ";
        read();
        solve();
    }
}