#include<bits/stdc++.h>
#define ll long long
#define all(a) (a).begin(),(a).end()
using namespace std;
const int maxn = 2e5 + 10;

int n, m;
int len;
ll v[maxn],du[maxn];
bool vis[maxn];
vector <ll> g[maxn];

void bfs(ll st)
{
    len=ceil(sqrt(n));
    for (int i=1; i<=n; i++) v[i]=-1;
    queue <ll> q;
    q.push(st);
    v[st]=0;
    vis[st]=1;
    while (q.size())
    {
        ll x=q.front();
        q.pop();
        if (v[x]>=len) continue;        
        for (int y:g[x])
        {
            if (v[y]==-1) {
                q.push(y);
                v[y]=v[x]+1;
                vis[y]=1;
            }
            else continue;
        }
    }
}
void bfs2(ll st)
{
    for (int i=1; i<=n; i++) v[i]=-1;
    queue <ll> q;
    q.push(st);
    v[st]=0;
    while (q.size())
    {
        ll x=q.front();
        q.pop();
        if (v[x]>=len) continue;      
        if (vis[x]==0) {
            vis[x]=1;
            for (int y:g[x]) {
                du[y]--;
            }
        }
        for (int y:g[x])
        {
            if (v[y]==-1) {
                q.push(y);
                v[y]=v[x]+1;
            }
            else continue;
        }
    }
}

void solve()
{
    cin >> n >> m;
    for (int i=1; i<=n+5; i++) 
    {
        g[i].clear();
        du[i]=0;
    }
    for (int i=1; i<=m; i++)
    {
        int u, v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
        du[u]++;
        du[v]++;
    }
    vector <ll> ans;
    while (1)
    {
        ans.clear();
        ll q=1;
        for (int i=1; i<=n+5; i++) vis[i]=0;
        while (q<=n) 
        {
            while (vis[q]) q++;
            if (q>n) break;
            ans.push_back(q);
            bfs(q);
            q++;
        }       
        if (ans.size()<=len) break;
// cerr<< "asd\n";
        for (int i=1; i<=n+5; i++) vis[i]=0;
        ans.clear();
        q=1;
        ll flag=1;
        while (flag)
        {
            flag=0;
            ll mxid=0,mxdu=-9999999999;
            for (int i=1; i<=n; i++)
            {
                if (vis[i]) continue;
                if (du[i]>mxdu){
                    mxdu=du[i];
                    mxid=i;
                }
                flag=1;
            }
            if (flag==0) break;
            bfs2(mxid);
            ans.push_back(mxid);
        }
        if (ans.size()<=len) break;        
        assert(0);
    }

    cout << ans.size() << "\n";
    for (int i=0; i<ans.size(); i++) cout << ans[i] << " ";
    cout << "\n";
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);cout.tie(nullptr);
    int t = 1;
    cin >> t;
    while(t--) solve();
    return 0;
}