bipartite

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

int n;
vector<bool> visited;
vector<int> red; // even
vector<int> blue; // odd
vector<vector<int>> graph;

void dfs(int source, int counter){
    if (visited[source]){
        return;
    }
    else{
        visited[source] = true;
        if (counter % 2 == 0){
            red.push_back(source);
        }
        else{
            blue.push_back(source);
        }
        for (int child : graph[source]){
            if (!visited[child]){
                dfs(child, (counter + 1)%2);
            }
        }
    }
}

int main(){
    int t;
    cin >> t;
    while(t--){
        int n, m;
        cin >> n >> m;
        for (int i = 0; i < m; i++){
            int u, v;
            cin >> u >> v;
        }
        dfs(0, 0);
        int red_nodes = red.size();
        int blue_nodes = blue.size();
        cout << min(red_nodes, blue_nodes) << endl;
        if (blue_nodes <= red_nodes){
            for (auto i : blue){
                cout << i << " ";
            }
        }
        else{
            for (auto i : red){
                cout << i << " ";
            }
        }
    }
}