#include<bits/stdc++.h>
using namespace std;
const int N=2e5+5;
int n,m,T,f[N],dep[N],w[N],mx[N],k,s[N];
int fi(int x){return x==f[x]? x:f[x]=fi(f[x]);}
vector<int>E[N],ans;
void dfs(int x,int f){
    // printf("___%d %d\n",x,f);
    dep[x]=dep[f]+1;
    mx[x]=dep[x];
    for(auto to:E[x]){
        if(to==f)continue;
        dfs(to,x);
        mx[x]=max(mx[x],mx[to]);
    }
    if(!f||mx[x]-dep[x]==k){
        ans.push_back(x);
        mx[x]=dep[x]-1;
    }
}
void slv(){
    scanf("%d %d",&n,&m);
    k = 1;
    while(k * k < n) k ++;
    ans.clear();
    for(int i=1;i<=n;++i)E[i].clear();
    for(int i=1;i<=n;++i)f[i]=i,s[i]=0;
    for(int i=1;i<=m;++i){
        int x,y;
        scanf("%d %d",&x,&y);
        if(fi(x)==fi(y))continue;
        f[fi(x)]=fi(y);
        s[x]++,s[y]++;
        E[x].push_back(y);
        E[y].push_back(x);
    }
    int rt=1;
    for(int i=1;i<=n;++i)if(s[i]==1)rt=i;
    dfs(rt,0);
    // if(ans.empty())ans.push_back(rt);
    assert(ans.size()<=k);
    printf("%d\n",(int)ans.size());
    for(auto x:ans)printf("%d ",x);
    puts("");
}
int main(){
    scanf("%d",&T);
    while(T--)slv();

}