#include<bits/stdc++.h>
using namespace std;
void mian()
{
	int n,m;
	cin>>n>>m;
	vector<int> pa(n+5);
	function<int(int)> find=[&](int x){return pa[x]?pa[x]=find(pa[x]):x;};
	vector<vector<int>> G(n+5);
	for(int i=1;i<=m;i++)
	{
		int u,v;
		cin>>u>>v;
		int pu=find(u),pv=find(v);
		if(pu!=pv)
		{
			G[u].push_back(v),G[v].push_back(u);
			pa[pv]=pu;
		}
	}
	vector<int> dep(n+5);
	function<void(int)> dfs=[&](int u)
	{
		for(auto v:G[u])
		{
			if(not dep[v])
			{
				dep[v]=dep[u]+1;
				dfs(v);
			}
		}
	};
	dep[1]=1;
	dfs(1);
	int s=sqrt(n);
	while(s*s<n)s++;
//	cerr<<s<<endl;
	vector<vector<int>> dg(s+5);
	for(int i=1;i<=n;i++)
	{
		dg[dep[i]%s].push_back(i);
	}
	for(int i=0;i<s;i++)
	{
		if((int)dg[i].size()==0)
		{
			cout<<1<<"\n";
			cout<<1<<"\n";
			return;
		}
		if((int)dg[i].size()<=s)
		{
			cout<<dg[i].size()<<"\n";
			for(auto x:dg[i])
				cout<<x<<' ';
			cout<<"\n";
			return;
		}
	}
	return;
}
int main()
{
	ios_base::sync_with_stdio(false);
	int T;
	cin>>T;
	while(T--)
	{
		mian();
	}
	return 0;
}