#include <bits/stdc++.h>

using i64 = long long;

void solve() {
    int n, m;
    std::cin >> n >> m;

    std::vector<std::vector<int>> adj(n);
    for (int i = 0; i < m; i ++ ) {
        int u, v;
        std::cin >> u >> v;
        u --, v -- ;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    std::vector<std::vector<int>> nadj(n);
    std::vector<bool> vis(n);
    auto dfs = [&](auto self, int x) -> void {
        vis[x] = 1;
        for (auto y : adj[x]) {
            if (!vis[y]) {
                nadj[x].emplace_back(y);
                nadj[y].emplace_back(x);
                self(self, y);
            }
        }
    };
    dfs(dfs, 0);

    int t = std::ceil(std::sqrt(n));

    std::vector<int> s;
    std::vector<int> dep(n);
    auto dfs1 = [&](auto self, int x, int p) -> void {
        for (auto y : nadj[x]) {
            if (y == p) {
                continue;
            }
            self(self, y, x);
            dep[x] = std::max(dep[x], dep[y] + 1);
        }
        if (!x || dep[x] >= t) {
            dep[x] = 0;
            s.push_back(x);
        }
    };
    dfs1(dfs1, 0, -1);

    std::cout << s.size() << "\n";
    for (auto x : s) {
        std::cout << x + 1 << " ";
    }
    std::cout << "\n";
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int t;
    std::cin >> t;

    while (t -- ) {
        solve();
    }

    return 0;
}