#include <bits/stdc++.h>
using namespace std;
#define int long long
int visited[2000090];
vector<int>edges[2000090];
vector<int>ans;
int n;
void bfs(int start)
{
    int tok=1;
    vector<pair<int,int>>que;
    int index=0;
    que.push_back(make_pair(start,1));
    visited[start]++;
    ans.push_back(start);
    int last_index=0;
    while(index!=n)
    {
        while(index<=last_index)
        {
            int s=que[index].first;
            for(auto x:edges[s]){
                if(visited[x]==0){
                    // cout<<"check "<<s<<" "<<x<<endl;
                    if(!tok){
                        ans.push_back(x);
                    }
                    visited[x]=1;
                    que.push_back(make_pair(x,tok^1));
                }
            }
            index++;
        }
        last_index=que.size()-1;
        tok^=1;
    }
}
main()
{
    int q;
    cin>>q;
    while(q--){
        ans.clear();
        int m;
        cin>>n>>m;
        vector<pair<int,int> >degree;
        for(int i=1;i<=n;i++){
            edges[i].clear();
            degree.push_back(make_pair(0,i));
        }
        for(int i=0;i<m;i++){
            int u,v;
            cin>>u>>v;
            degree[u].first++;
            degree[v].first++;
            edges[u].push_back(v);
            edges[v].push_back(u);
        }
        // cout<<"edges\n";
        // for(int i=1;i<=n;i++)
        // {
        //     cout<<"i="<<i<<endl;
        //     for(auto x:edges[i]){
        //         cout<<x<<" ";
        //     }
        //     cout<<endl;
        // }
        memset(visited,0,sizeof(visited));
        sort(degree.begin(),degree.end());
        int start=degree[degree.size()-1].second;
        // cout<<start<<endl;
        bfs(start);
        // cout<<"ans\n";
        cout<<ans.size()<<endl;
        for(auto x:ans){
            cout<<x<<" ";
        }
        cout<<endl;
    }
}