#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], mx, dis[N];
vector<ll> edge[N], ans;

void init(){
    for (int i = 0; i <= n; i++)fa[i] = i, edge[i].clear(), dis[i] = 1e18;
    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);
    fa[x] = fa[y];
}

void dfs(ll x, ll fa){
    // cerr << x << " " << fa << endl;
    dis[x] = min(dis[x], dis[fa] + 1);
    if (dis[x] >= mx){
        ans.push_back(x);
        dis[x] = 0;
    }
    for (auto i : edge[x]){
        if (i == fa)continue;
        dfs(i, x);
        dis[x] = min(dis[x], dis[i] + 1);
    }
}

inline void solve(){
    cin >> n >> m;
    init();
    // cerr << n << " " << m << endl;
    for (int i = 1, u, v; i <= m; i++){
        cin >> u >> v;
        if (find(u) == find(v))continue;
        merge(u, v);
        edge[u].push_back(v);
        edge[v].push_back(u);
        // cerr << u << " " << v << endl;
    }
    dfs(1, 0);
    assert(ans.size() <= mx);
    cout << ans.size() << endl;
    for (auto i : ans)cout << i << " ";
    cout << endl;
    // cerr << n << " " << m << endl;
}



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