#include <bits/stdc++.h>
using namespace std;

const int maxn=200000;

int T;
int n,m;
vector<int> g[maxn+50];
int dis[maxn+50];

int main(){
	ios_base::sync_with_stdio(false);
	cin >> T;
	for (;T--;){
		cin >> n >> m;
		int S=sqrt(n);
		for (;S*S<n;) S++;
		for (;(S-1)*(S-1)>=n;) S--;
		
		int B=n/S;
		
		for (int i=1;i<=m;i++){
			int x,y;
			cin >> x >> y;
			g[x].push_back(y);
			g[y].push_back(x);
		}
		for (int i=1;i<=n;i++) dis[i]=-1;
		queue<int> q;
		q.push(1);
		dis[1]=0;
		for (;!q.empty();){
			int u=q.front();
			q.pop();
			for (auto v:g[u]){
				if (dis[v]!=-1) continue;
				dis[v]=dis[u]+1;
				q.push(v);	
			}
		}
		vector<pair<int,int>> perm(n+1);
		for (int i=1;i<=n;i++) perm[i]=make_pair(dis[i],i);
		sort(perm.begin()+1,perm.begin()+n);
		vector<int> ans;
		for (int i=1;i<=S;i++) ans.push_back(perm[(i-1)*B+1].second);
		cout << ans.size() << "\n";
		for (auto e:ans) cout << e << " ";
		cout << "\n";
		
		for (int i=1;i<=n;i++){
			dis[i]=-1;
			g[i].clear();	
		}
	}
	return 0;	
}