#include <bits/stdc++.h> 
using namespace std;
#define f first
#define s second
int main(){
	long long zz;
	cin>>zz;
	while(zz--){
		long long n,m;
		cin>>n>>m;
		vector<long long> adj[n];
		vector<bool> visited(n,0);
		vector<long long> depth(n,-1);
		set<long long> stt,poss;
		long double d = sqrtl(n);
    	long long bor = d;
   	    if(bor < d) bor++;
		for(long long i=0;i<m;i++){
		long long x,y;
		cin>>x>>y;
		x--;y--;
		adj[x].push_back(y);
		adj[y].push_back(x);
		}
		queue<int> q;
		int y=rand();
		y%=n;
		stt.insert(y);
		visited[y]=1;
		q.push(y);
		depth[y]=0;
		while(!q.empty()){
		while(!q.empty()){
			int v=q.front();
			q.pop();
			for(auto x:adj[v]){
				if(!visited[x]){
					q.push(x);
					visited[x]=1;
					depth[x]=1+depth[v];}
			}
		}
		for(int i=0;i<n;i++){
			if(depth[i]>bor){
				visited[i]=0;
				depth[i]=-1;
			}
			if(depth[i]==bor){
				poss.insert(i);
				visited[i]=0;
			}
		}
		for(auto x:poss){
			if(!visited[x]){
				stt.insert(x);
				depth[x]=0;
				visited[x]=1;
				q.push(x);
				break;
			}
		}
		}
		cout<<stt.size()<<'\n';
		for(auto x:stt){
			cout<<x<<' ';
		}
		cout<<'\n';
		
	}
	return 0;
}