#include <bits/stdc++.h>
using namespace std;
#define int long long

class DSU {
public:
    int n;
    vector <int> p;
    
    DSU(int _n) {
        n = _n;
        p.resize(n);
        iota(p.begin(), p.end(), 0);
    }

    int find(int x) {
        if(x == p[x]) return x;
        return p[x] = find(p[x]);
    }

    bool unite(int a, int b) {
        if(find(a) != find(b)) {
            p[find(b)] = find(a);
            return true;
        } 
        return false;
    }
};

vector<bool> col;
int sq;
vector<vector<int>> adj;

int dfs(int node, int prev) {
    if(node != prev && (int)adj[node].size() == 1) return 1;
    int mx = 0;
    for(auto next : adj[node]) if(next != prev) mx = max(mx, dfs(next, node));
    if(mx == sq || node == prev) {
        col[node] = true;
        return 1;
    }
    return mx + 1;
}

int32_t main() {
    cin.tie(0)->sync_with_stdio(0);

    int t;
    cin >> t;
    while(t--) {
        int n, m;
        cin >> n >> m;
        adj.clear();
        adj.resize(n);
        DSU d(n);
        // Directly make an MST
        for(int i = 0; i < m; i++) {
            int x, y;
            cin >> x >> y;
            --x; --y;
            if(d.unite(x, y)) {
                adj[x].push_back(y);
                adj[y].push_back(x);
            }
        }
        col.clear();
        col.resize(n, false);
        sq = sqrt(n);
        if(sq * sq < n) sq++;
        dfs(0, 0);
        int ans = 0;
        for(auto i : col) if(i) ans++;
        assert(ans <= sq);
        cout << ans << '\n';
        for(int i = 0; i < n; i++) {
            if(col[i]) cout << i + 1 << ' ';
        }
        cout << '\n';
    }


}