#include <bits/stdc++.h>

using namespace std;

#define io ios_base::sync_with_stdio(false); cin.tie(0); cerr.tie(0)
#define iter(v) v.begin(), v.end()
#define SZ(v) int(v.size())
#define pb emplace_back
#define mp make_pair
#define ff first
#define ss second

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

#ifdef zisk
void debug(){cerr << "\n";}
template<class T, class ... U>
void debug(T a, U ... b){cerr << a << " ", debug(b...);}
template<class T> void pary(T l, T r){
	while(l != r) cerr << *l << " ", l++;
	cerr << "\n";
}
#else
#define debug(...) void()
#define pary(...) void()
#endif
template<class A, class B>
ostream& operator<<(ostream& o, pair<A, B> p){
	return o << '(' << p.ff << ',' << p.ss << ')';
}
const int maxn = 200005;

vector<int> adj[maxn];
bool vis[maxn];
bool ans[maxn];
int dep[maxn];
int K, tot;

void dfs(int n) {
	vis[n] = 1;
	for (int v:adj[n]) {
		if (!vis[v]) {
			dfs(v);
			dep[n] = max(dep[n], dep[v] + 1);
		}
	}
	if (dep[n] >= K || n == 1) {
		ans[n] = 1;
		dep[n] = 0;
		tot++;
	}
}
int main(){
	io;

	int t;
	cin >> t;
	while (t--) {
		int n, m;
		cin >> n >> m;
		for (int i = 1;i <= n;i++) vis[i] = 0, adj[i].clear(), ans[i] = 0, dep[i] = 0;
		for (int i = 1;i <= n;i++) {
			if (i*i >= n) {
				K = i;
				break;
			}
		}
		for (int i = 0;i < m;i++) {
			int u, v;
			cin >> u >> v;
			adj[u].push_back(v);
			adj[v].push_back(u);
		}
		tot = 0;
		dfs(1);	
		assert(tot <= K);
		cout << tot << "\n";
		for (int i = 1;i <= n;i++) {
			if (ans[i]) cout << i << " ";
		}
		cout << "\n";
	}

}