#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> PII;
#define Yes cout<<"YES\n"
#define No  cout<<"NO\n"
#define all(a) a.begin(),a.end()
#define pb push_back
#define endl '\n'
//#define int ll
const ll mod=1e9+7;const int M=2e5+5;const int N=2e5+5;
int dx[] = {-1, 1, 0, 0};int dy[] = {0, 0, -1, 1};
vector<int> g[N];queue<int> q;
vector<int> tr[N];
set<int> ans;
int dep[N],vis[N],k;
void dfs(int u,int fa){
    for(auto v:tr[u]){
        if(v==fa) continue;
        dfs(v,u);
        dep[u]=max(dep[u],dep[v]+1);
    }
    if(dep[u]>=k){
        ans.insert(u);
        dep[u]=-1;
    }
}
void solve()
{
    int n,m;cin>>n>>m;
    k=ceil(sqrt(n));
    ans.clear();
    for(int i=1;i<=n;i++){
        g[i].clear();
        tr[i].clear();
        vis[i]=0;
        dep[i]=0;
    }
    for(int i=1;i<=m;i++){
        int x,y;cin>>x>>y;
        g[x].pb(y);
        g[y].pb(x);
    }
    q.push(1);
    while(q.size()){
        int u=q.front();q.pop();
        if(vis[u]) continue;
        vis[u]=1;
        for(auto v:g[u]){
            if(vis[v]) continue;
            q.push(v);
            tr[u].pb(v);
        }
    }
    dfs(1,0);
    if(ans.count(1)==0&&ans.size()<k) ans.insert(1);
    cout<<ans.size()<<endl;
    for(auto v:ans) {
        cout<<v<<' ';
    }cout<<endl;
}
signed main()
{
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int __;
    __=1;
    cin>>__;
    while(__--)
    {
    solve();
    }
}