#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define endl '\n'
const int N=2e5+5;
int n,m,depth[N],dis;
vector<int>to[N],ans;
void bfs(int u){
	queue<int>q;
	q.push(u);
	depth[u]=0;
	ans.push_back(u);
	while(!q.empty()){
		u=q.front();q.pop();
		for(auto v:to[u])
		{
			if(depth[v]==-1){
				depth[v] = depth[u]+1 , q.push(v);
				if(depth[v] % (dis+1) == 0)  ans.push_back(v);
			}
				
		}
			
	}
}
void solve(){
	cin>>n>>m;
	dis=ceil(sqrt(n));
	for(int i=1;i<=n;i++){
		depth[i]=-1;
		to[i].clear();
	}
	ans.clear();
	for(int i=1;i<=m;i++){
		int u,v;
		cin>>u>>v;
		to[u].push_back(v);
		to[v].push_back(u);
	}
	bfs(1);
	cout<<ans.size()<<endl;
	for(auto it:ans)cout<<it<<" ";
	cout<<endl;
}
int main(){
	int _=1;
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	cin>>_;
	while(_--)
	solve();
	return 0;
}