#include<bits/stdc++.h>

int main() {
	using namespace std;
	cin.tie(nullptr)->sync_with_stdio(false);
	int T; cin >> T;

	while (T--) {
		int N, M; cin >> N >> M;
		
		vector<vector<int>> adj(N);
		for (int i = 0; i < M; ++i) {
			int a, b; cin >> a >> b;
			--a, --b;
			adj[a].push_back(b);
			adj[b].push_back(a);
		}
		
		cerr << endl;
		vector<vector<int>> tree(N);
		vector<bool> vis(N); vis[0] = true;
		vector<int> bfs = {0}; bfs.reserve(N);
		for (int z = 0; z < int(bfs.size()); ++z) {
			int cur = bfs[z];
			for (int nxt : adj[cur]) {
				if (vis[nxt]) continue;
				vis[nxt] = true;
				// cerr << cur << ' ' << nxt << endl;
				tree[cur].push_back(nxt);
				tree[nxt].push_back(cur);
				bfs.push_back(nxt);
			}
		}

		int sqn = 1;
		while (sqn * sqn <= N) sqn += 1;
		
		// cerr << "sqrt  " << sqn << endl;
		vector<int> depth(N); depth[0] = 1;
		auto dfs = [&](auto&& self, int cur) -> void {
			for (int nxt : tree[cur]) {
				if (depth[nxt]) continue;
				depth[nxt] = depth[cur] + 1;
				self(self, nxt);
			}
		};
		
		dfs(dfs, 0);

		/*
		for (int i = 0; i < N; ++i) {
			cerr << depth[i] << endl;
		}
		*/

		vector<vector<int>> loc(sqn, {0});
		for (int i = 0; i < N; ++i) {
			loc[depth[i] % sqn].push_back(i);
		}

		for (int i = 0; i < sqn; ++i) {
			int s = int(loc[i].size());
			if (s <= sqn) {
				cout << s << '\n';
				for (int j = 0; j < s; ++j) {
					cout << loc[i][j] + 1 << " \n"[j == s-1];
				}
				break;
			}
		}
	}
}