#include<bits/stdc++.h>
using namespace std;
const int N = 2e5+10;
vector<int> v[N];
int a[N], b[N];
int dis[N];
bool vis[N];
int n, m;
int x, y;
int ed, mxdis;
void bfs(int st){
    for(int i = 1;i <= n;i++){
        vis[i] = 0;
        dis[i] = 0;
    }
    mxdis= 0;
     queue<int> q;
     q.push(st);
     dis[st] = 0;
     vis[st] = 1;
     while(!q.empty()){
        int x = q.front();
        q.pop();
        for(auto y : v[x]){
            if(vis[y]) continue;
            vis[y] = 1;
            dis[y] = dis[x] +1;
            if(dis[y] > mxdis){
                mxdis = dis[y];
                ed = y;
            }
            q.push(y);
        }
     }
}
int main(){
   int tt;
   cin >> tt;
   while(tt--){
    cin >> n >> m;
    int k = ceil(sqrt(n));
    for(int i = 1;i <= m;i++){
         cin >>x >> y;
         v[x].emplace_back(y);
         v[y].emplace_back(x);
    }
    if(n == 1){
        cout << "1\n1\n";
        continue;
    }
        bfs(1);
        int st = ed;
        bfs(st);
        vector<int> ans;
        for(int i = 1;i <= n;i++){
            if(dis[i] && dis[i]%k == 0){
               ans.push_back(i);
            }
        }
        if(ans.size() == 0){
            ans.push_back(1);
        }
        cout << ans.size() << "\n";
        for(auto x : ans){
            cout <<x << " ";
        }
        cout << "\n";
   }
   return 0;
}