#include <bits/stdc++.h> 
using namespace std;
#define f first
#define s second
int n,m;
vector<int> adj[200005];
vector<bool> visited(200005,0);
vector<int> ans;
void dfs(int i){
	ans.push_back(i);
	visited[i]=1;
	for(auto x: adj[i]){
		if(!visited[x]){
			dfs(x);
		}
	}
	return ;
}
int main(){
	int zz;
	cin>>zz;
	while(zz--){
		cin>>n>>m;
		for(int i=0;i<m;i++){
			int x,y;
			cin>>x>>y;
			x--;y--;
			adj[x].push_back(y);
			adj[y].push_back(x);
		}
		dfs(0);
		int jmp;
		for(int i=0;i<n;i++){
			if(i*i>=n)
				{jmp=i;break;}
		}
		//cout<<jmp;
		cout<<n/jmp<<'\n';
		for(int i=0;i<ans.size();i+=jmp){
			cout<<1+ans[i]<<' ';
		}
		cout<<'\n';
		ans.clear();
		for(int i=0;i<n;i++){
			adj[i].clear();
			visited[i]=0;
		}
	}
	return 0;
}