#include <bits/stdc++.h>
#define rep(i,l,r) for(int i=l; i<=r; i++)
#define IOS {cin.tie(0);cout.tie(0);ios::sync_with_stdio(0);}
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
const int N=2e5+5;
int fa[N],dep[N];
vector<int>tu[N],ans[N];
int fd(int x){
    if(x==fa[x])return x;
    return fa[x]=fd(fa[x]);
}
void dfs(int now,int pre){
    dep[now]=dep[pre]+1;
    for(int son:tu[now]){
        if(son==pre)continue;
        dfs(son,now);
    }
}
void slv(){
    int n,m;cin>>n>>m;
    ans[0].clear();
    rep(i,1,n){
        fa[i]=i; tu[i].clear(); ans[i].clear();
    }
    rep(i,1,m){
        int u,v;cin>>u>>v;
        int uu=fd(u),vv=fd(v);
        if(uu!=vv){
            fa[uu]=vv; tu[u].push_back(v); tu[v].push_back(u);
        }
    }
    dfs(1,0);
    int sn=sqrt(n);
    while(sn*sn<n)++sn;
    rep(i,1,n){
        ans[dep[i]%sn].push_back(i);
    }
    rep(i,0,sn-1){
        // cout<<i<<" "<<ans[i].size()<<endl;
        // if(i==0)cout<<ans[i].size()<<"hh\n";
        if(ans[i].size() && ans[i].size()<=sn){
            cout<<ans[i].size()<<'\n';
            for(auto v:ans[i])cout<<v<<' '; cout<<'\n';return;
        }
    }
    assert(0);
}
int main() {
    IOS
    int T;cin>>T;
    while(T--)slv();

    return 0;
}
/*
1 
5 4
1 2
2 3
3 4
4 5

2
4 3
1 2
2 3
3 4

6 7
1 2
2 3
3 1
1 4
4 5
5 6
6 4
*/