#include<bits/stdc++.h>
#define Gc() getchar() 
#define Me(x,y) memset(x,y,sizeof(x))
#define Mc(x,y) memcpy(x,y,sizeof(x))
#define d(x,y) ((m)*(x-1)+(y))
#define R(n) (rnd()%(n)+1)
#define Pc(x) putchar(x)
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
using namespace std;using ll=long long;using db=double;using lb=long db;using ui=unsigned;using ull=unsigned long long;using pii=pair<int,int>;using LL=__int128;
const int N=2e5+5,M=(1<<15)+5,K=14348907+5,mod=998244353,Mod=mod-1;const db eps=1e-9;const int INF=1e9+7;mt19937 rnd(time(0));
int n,m,x,y,k,tg[N];vector<int> S[N];
vector<int> ans;
int dfs(int x){
	if(tg[x]) return -1;tg[x]=1;
	int Le=0;
	for(int i:S[x]) Le=max(Le,dfs(i)+1);
	if(Le==k) ans.emplace_back(x),Le=0;
	return Le;
}
void Solve(){
	int i,j;ans.clear();fill(tg+1,tg+n+1,0);for(i=1;i<=n;i++) S[i].clear();
	scanf("%d%d",&n,&m);k=ceil(sqrt(n));
	while(m--) scanf("%d%d",&x,&y),S[x].emplace_back(y),S[y].emplace_back(x);
	dfs(1);
	printf("%d\n",ans.size());
	for(auto i:ans) printf("%d ",i);printf("\n");
}
int main(){
	int t;
	scanf("%d",&t);
	// t=1;                                                                                       
	while(t--) Solve();
	cerr<<clock()*1.0/CLOCKS_PER_SEC<<'\n';
}