#include<bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a),i##z=(b);i<=i##z;i++)
#define ROF(i,a,b) for(int i=(a),i##z=(b);i>=i##z;i--)
#define REP(i,u) for(int i=hd[u],v;v=to[i],i;i=nxt[i])
#define temT template<typename T>
#define temT12 template<typename T1,typename T2>
using namespace std;
typedef pair<int,int> pii;
typedef long long ll;
typedef long double ld;
const int N=int(2e5)+10;

temT void clearDS(T &x){ T y; swap(x,y); }

int T,n,m,B; vector<int> edg[N]; int deg[N];
queue<int> leaf,ans; int vis[N],tim;

void dfs(int t,int dis){
	if(dis>B) return ;
//	if(vis[t]==tim) return ;
	vis[t]=tim; deg[t]=0;
//	for(int v:edg[t]) if(vis[v]<tim){
	for(int v:edg[t]){
		if(vis[v]<tim) deg[v]--;
		dfs(v,dis+1);
	}
}

int main(){
	for(cin>>T;T--;){
		cin>>n>>m; B=ceil(sqrt(1.0*n));
		FOR(i,1,n) deg[i]=0,clearDS(edg[i]); clearDS(leaf),clearDS(ans);
		for(int i=1,u,v;i<=m;i++)
			cin>>u>>v,edg[u].push_back(v),edg[v].push_back(u),deg[u]++,deg[v]++;
		FOR(i,1,n) leaf.push(i);
		
		tim++;
		while(leaf.size()){
			int t=leaf.front(); leaf.pop(); 
			if(vis[t]==tim) continue;
			dfs(t,0); ans.push(t);
		}
		
		cout<<ans.size()<<"\n";
		while(ans.size()) (cout<<ans.front()<<" "),ans.pop();
		cout<<"\n";
	}
	return 0;
}