#include<bits/stdc++.h>
#define pll pair<ll, ll>
using namespace std;
typedef long long ll;
#define int ll

const int N = 1e5+10;
const int M = 1e6 + 7;

int n, m, fa[N], vis[N], mx;
vector<ll> edge[N], ans;

void init(){
    for (int i = 1; i <= n; i++)fa[i] = i, vis[i] = 0, edge[i].clear();
    ans.clear();
    mx = sqrt(n);
    if (mx * mx < n)mx++;
}

ll find(ll x){
    return x == fa[x] ? x : fa[x] = find(fa[x]);
}

void merge(ll x, ll y){
    x = find(x);
    y = find(y);
}

inline void solve(){
    cin >> n >> m;
    init();
    for (int i = 1, u, v; i <= m; i++){
        cin >> u >> v;
        u = find(u), v = find(v);
        if (u == v)continue;
        merge(u, v);
        edge[u].push_back(v);
        edge[v].push_back(u);
    }
    priority_queue<pll, vector<pll>, greater<pll>> q;
    q.push({n + 1, 1});
    while (q.size()){
        pll temp = q.top();
        q.pop();
        ll dis = temp.first, x = temp.second;
        if (vis[x])continue;
        vis[x] = 1;
        if (dis > mx){
            ans.push_back(x);
            dis = 0;
        }
        for (auto i : edge[x]){
            if (vis[i])continue;
            q.push({dis + 1, i});
        }
    }
    assert(ans.size() <= mx);
    cout << ans.size() << endl;
    for (auto i : ans)cout << i << " ";
    cout << endl;
}



signed main(){
    ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
    int WTN666=1;cin>>WTN666;
    while(WTN666--){
        solve();
    }
}