#include<bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define pb push_back
#define fi first
#define se second
#define endl "\n"


vector<int> v[200005];
int par[200005];
int Find(int x)
{
    if(par[x]==x) return x;
    return par[x] = Find(par[x]);
}
void Union(int a,int b)
{
    par[Find(a)] = Find(b);
}

void solve()
{
    int n,m;
    cin>>n>>m;
    vector<pii> edge;
    for(int i=0;i<m;i++)
    {
        int a,b;
        cin>>a>>b;
       edge.pb({a,b});
    }
    for(int i=0;i<=n;i++) par[i]=i;
    for(int i=0;i<m;i++)
    {
        int a=edge[i].first,b=edge[i].second;
        if(Find(a) != Find(b))
        {
            v[a].pb(b);
            v[b].pb(a);
            Union(a,b);
        }

    }
    set<int> s;
    for(int i=1;i<=n;i++) s.insert(i);
    int vis[n+1]={0};
    int sqr=sqrt(n);
    vector<int> ans;
    while(s.size())
    {
        int root=*s.begin();
        s.erase(s.begin());
        ans.pb(root);
        vector<int> tmp;
        queue<pii> q;
        q.push({root,0});

        while(!q.empty())
        {
            pii p =q.front();
            q.pop();
            for(auto i:v[p.fi]){
                if(vis[i]) continue;
                if(p.se+1> sqr) continue;
                q.push({i,p.se+1});
                vis[i]=1;
                tmp.pb(i);
            }
        }
        for(int i:tmp) vis[i]=0;
        for(int i:tmp)
        {
            if(s.find(i) != s.end()) s.erase(i);
        }

    }
    cout<<ans.size()<<endl;
    for(int i:ans) cout<<i<<' ';
    cout<<endl;
    for(int i=0;i<=n;i++) v[i].clear();
}

int main()
{
    int tc;
    cin>>tc;
    while(tc--)
    {
        solve();
    }
}