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

const int N = 200005;
int fa[N],n,m;
int find(int u) {return fa[u]==u?u:fa[u]=find(fa[u]);}
vector<int> md[N],G[N];
int dep[N],sq;
void dfs(int u,int f)
{
	dep[u]=dep[f]+1;
	md[dep[u]%sq].push_back(u);
	for(int v:G[u])
	{
		if(v==f) continue;
		dfs(v,u);
	}
}
void work()
{
	scanf("%d %d",&n,&m);
	for(int i=0;i<=n;i++) fa[i]=i,G[i].clear(),md[i].clear();
	for(int i=1;i<=m;i++)
	{
		int u,v; scanf("%d %d",&u,&v);
		if(find(u)==find(v)) continue;
		// printf("%d %d\n",u,v);
		G[u].push_back(v),G[v].push_back(u);
		fa[find(u)]=find(v);
	}
	sq=0;
	while(sq*sq<n) sq++;
	dep[0]=-1;
	dfs(1,0);
	for(int i=1;i<sq;i++) md[i].push_back(1);
	for(int i=0;i<sq;i++)
	{
		if((int)md[i].size()<=sq)
		{
			printf("%d\n",(int)md[i].size());
			for(int j=0;j<(int)md[i].size();j++) printf("%d%c",md[i][j]," \n"[j==(int)md[i].size()-1]);
			return ;
		}
	}
}

int main() {
#ifdef xay5421
	freopen("a.in","r",stdin);
#endif
	int T;
	scanf("%d", &T);
	while (T--) {
		work();
	}
	return 0;
}