#include <bits/stdc++.h>
#define x first
#define y second
using namespace std;
using pii=pair<int,int>;
using ll=long long;
using vi=vector<int>;
using vl=vector<ll>;
#define pb push_back
#define all(a) begin(a),end(a)

const int N=300010,MOD=1e9+7;
const char en='\n';
const ll LLINF=1ll<<60;

int t,n,m;
vi ch[N],id[N];
bool bio[N];

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cin>>t;
	while (t--)
	{
		cin>>n>>m;
		for (int i=0;i<=n;++i) ch[i].clear(),bio[i]=0,id[i].clear();
		int ko=1;
		while (ko*ko<n) ++ko;
		for (int i=0;i<m;++i)
		{
			int a,b;
			cin>>a>>b;
			ch[a].pb(b);
			ch[b].pb(a);
		}
		queue<pii> q;
		q.push({1,0});
		while (q.size())
		{
			int i=q.front().x,d=q.front().y;
			q.pop();
			if (bio[i]) continue;
			bio[i]=1;
			id[d%ko].pb(i);
			for (auto x: ch[i]) q.push({x,d+1});
		}
		for (int i=1;i<ko;++i) id[i].pb(1);
		for (int i=0;i<ko;++i) if (id[i].size()<=ko)
		{
			cout<<id[i].size()<<en;
			for (auto x: id[i]) cout<<x<<' ';
			cout<<en;
			break;
		}
	}
}