#include<bits/stdc++.h>
using namespace std;
const int N = 2e5+10;
vector<int> e[N];
vector<int> ans;
int dis[N];
int n, m, k;
int x ,y;
bool vis[N];
void bfs(int x){
     dis[x] = 0;
     vis[x] = 1;
     queue<int> q;
     q.push(x);
    while(!q.empty()){
        int u = q.front();
        q.pop();
        for(auto y : e[u]){
            if(vis[y]) continue;
            vis[y] = 1;
            dis[y] = dis[u] + 1;
            q.push(y);
        }
    }
    for(int i = 1;i <= n;i++){
        if(dis[i]%(k) == 0){
            ans.push_back(i);
        }
    }
    return ;
}
int main(){
    int tt;
    cin >> tt;
    while(tt--){
        cin >> n >>m;
        ans.clear();
        for(int i = 1;i <= n;i++){
                e[i].clear();
            vis[i] = 0;
            dis[i] = 0;
        }
        k = ceil(sqrt(n));
        for(int i = 1;i <= m;i++){
            cin >> x >> y;
            e[x].push_back(y);
            e[y].push_back(x);
        }
        bfs(1);
        cout << ans.size() << "\n";
        for(auto x : ans){
            cout << x << " ";
        }
        cout << "\n";
    }
    return 0;
}
/*
10000
15 14
13 12
5 4
9 8
11 12
15 14
10 9
14 13
2 3
2 1
6 5
10 11
3 4
7 6
8 7

6 5
2 1
2 4
4 6
2 3
3 5

10 9
8 3
9 4
5 6
5 10
3 2
5 4
2 7
1 2
4 3

2 1
2 1

2 1
2 1

9 8
9 8
5 4
1 2
6 5
3 4
3 2
7 8
7 6

2 1
1 2

14 13
3 10
5 6
2 9
11 4
2 3
2 1
8 7
13 6
5 4
5 12
6 7
4 3
7 14

16 15
2 3
2 1
6 10
6 9
6 4
9 11
*/