#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define ll long long

const int N = 2e5 + 5;

int n, m, rootN, added;
vector<int> adj[N];
bool vis[N];

void dfs(int u) {
    for(int v: adj[u]) {
        if(vis[v]) continue;
        vis[v] = 1;
        added++;
        if(added >= rootN) return;
        dfs(v);
    }
}

int root(int n) {
    int ret = sqrt(n);
    while(ret*ret < n) ret++;
    return ret;
}

int main() {
    ios_base::sync_with_stdio(false); cin.tie(NULL);

    int t;
    cin>> t;
    while(t--) {
        cin>> n >> m;
        for(int i=0; i<m; i++) {
            int u, v;
            cin>> u >> v;
            adj[u].push_back(v);
            adj[v].push_back(u);
        }
        rootN = root(n);
        vector<int> ans;
        for(int i=1; i<=n; i++) {
            if(vis[i]) continue;
            vis[i] = 1;
            ans.push_back(i);
            added = 0;
            dfs(i);
        }
        cout<< ans.size() << endl;
        for(int e: ans) cout<< e << " "; cout<< endl;
        for(int i=0; i<=n; i++) {
            adj[i].clear();
            vis[i] = 0;
        }
    }
}