#include<bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define PI acos(-1)
#define io ios::sync_with_stdio(false); cin.tie(0); cout.tie(0)
#define mem(a,b) memset((a),(b),sizeof(a))
typedef long long ll;
typedef unsigned long long ull;
#define int long long
#define db long double

const double eps = 1e-6;
const int mod = 1e9 + 7;
const int maxn = 1e6 + 10;
int n, m, d[maxn], vis[maxn], len;
vector<int> dep[maxn];
vector<int> edge[maxn];
vector<int> e[maxn];
set<int> ans, temp;

void bfs(int u) {
    queue<int> que;
    que.push(u);
    vis[u] = 1;
    dep[1].push_back(u);
    while(!que.empty()) {
        int now = que.front();
        que.pop();
        for(int i = 0; i < edge[now].size(); i++) {
            int v = edge[now][i];
            if(vis[v] == 0) {
                vis[v] = vis[now] + 1;
                e[now].push_back(v);
                e[v].push_back(now);
                dep[vis[v]].push_back(v);
                que.push(v);
            }
        }
    }
}

void dfs(int now, int fa, int deep) {
    if (deep % (2 * len + 1) == 0) {
        ans.insert(now);
    }
    if (deep % (2 * len + 1) > len) {
        ans.insert(now);
        return ;
    }
    for (auto chd : e[now]) {
        if (chd == fa) continue;
        dfs(chd, now, deep + 1);
    }
}

void solve() {
    ans.clear();
    cin >> n >> m;
    if(m == 0) {
        cout << 1 << '\n';
        cout << 1 << '\n';
        return;
    }
    for(int i = 0; i <= n; i++) e[i].clear(), vis[i] = 0, edge[i].clear(), dep[i].clear();
    for(int i = 0, u, v; i < m; i++) {
        cin >> u >> v;
        edge[u].push_back(v);
        edge[v].push_back(u);
    }
    bfs(1);
    // cerr << pos << '\n';
    // for(int i = 1; i <= n; i++) {
    //     cerr << i << ": " << vis[i] << '\n';
    // }
    len = (int)ceil(sqrt(n));
    dfs(1, -1, 0);
    cout << ans.size() << '\n';
    for (auto i : ans) {
        cout << i << ' ';
    }
    cout << '\n';
}

signed main(){
    io;
        int T = 1;
        cin >> T;
        while(T--) {
            solve();
        }
        return 0;
}