#include <bits/stdc++.h>

using namespace std;
using PII = pair<int,int>;
using ll = long long;

constexpr int N = 2e6 + 10;
vector<int> ans;
vector<int> e[N];
int d[N];
ll k;
void dfs(int u, int cnt) {
	if(cnt % (k + 1) == 0) ans.push_back(u);
	d[u] = 1;
	for(auto v : e[u]) {
		if(d[v] == -1) {
			dfs(v, cnt + 1);
		}
	}
}

void solve() {
	int n, m;
	cin >> n >> m;
	k = ceil(sqrt(n));
	ans.clear();
	for(int i = 1; i <= n; i ++) e[i].clear(), d[i] = -1;
	for(int i = 1; i <= m; i ++) {
		int u, v;
		cin >> u >> v;
		e[u].push_back(v);
		e[v].push_back(u);
	}
	dfs(1, 0);
	cout << ans.size() << "\n";
	for(auto v : ans) {
		cout << v << " ";
	}
	cout << "\n";
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int t;
	t = 1;
	cin >> t;
	while(t --){
		solve();
	}
}