#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 2e6 + 10;
const int mod = 1e9 + 7;

vector<int> e[N], ans;
int vis[N], f[N], dep[N];
struct node {
    int dep, id;
    bool operator<(const node &x) const {
        return dep > x.dep;
    }
} a[N];

void dfs1(int u, int fa) {
    vis[u] = 1;
    a[u].dep = a[fa].dep + 1;
    f[u] = fa;
    for (auto v : e[u]) {
        if (v == fa || vis[v]) continue;
        dfs1(v, u);
    }
}
int limit;
void dfs2(int u, int fa, int dis) {
    vis[u] = 1;
    if (dis == limit) return;
    for (auto v : e[u]) {
        // if (vis[v]) continue;
        dfs2(v, u, dis + 1);
    }
}

void solve() {
    int n, m;
    cin >> n >> m;
    limit = sqrt(n);
    limit += (limit * limit != n);
    for (int i = 1; i <= n; ++i) {
        a[i].dep = 0;
        vis[i] = 0;
        e[i].clear();
        a[i].id = i;
    }
    ans.clear();
    for (int i = 1; i <= m; ++i) {
        int u, v;
        cin >> u >> v;
        e[u].emplace_back(v);
        e[v].emplace_back(u);
    }
    dfs1(1, 0);
    for (int i = 1; i <= n; ++i) vis[i] = 0;
    sort(a + 1, a + n + 1);
    for (int i = 1; i <= n; ++i) {
        if (!vis[i]) {
            int u = a[i].id;
            int tot = 0;
            while (tot < limit && f[u] != 0) {
                u = f[u];
                tot++;
            }
            ans.emplace_back(u);
            dfs2(u, f[u], 0);
        }
    }
    cout << ans.size() << "\n";
   
    for (auto i : ans) cout << i << " ";
    cout << "\n";
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cout.tie(nullptr);
    int _;
    std::cin >> _;
    while (_--)
        solve();
    return 0;
}