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

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define PB push_back
#define FS first
#define SD second
#define cmx(x,y) x = max(x,y)
#define cmn(x,y) x = min(x,y)
#define ary(k) array<int,k>
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

vi kra[1000002];
int dp[1000002], odw[1000002];
vi ans;

void dfs(int n, int sq) {
    odw[n] = 1;
    int maxdep = 0;
    for (auto v : kra[n]) {
        if (odw[v]) continue;
        dfs(v, sq);
        cmx(maxdep, dp[v]+1);
    }
    if (maxdep == sq) {
        ans.PB(n);
        dp[n] = -1;
    } else {
        dp[n] = maxdep;
    }
}

void fun() {
    ans.clear();
    int n, m, sq;
    cin >> n >> m;
    sq = sqrt(n);
    if (sq * sq < n) sq++;
    for (int i = 1; i <= n; i++) {
        kra[i].clear();
        odw[i] = 0;
    }
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        kra[a].PB(b);
        kra[b].PB(a);
    }
    dfs(1, sq);
    if (ans.empty()) ans.PB(1);
    cout << ans.size() << "\n";
    for (auto v : ans) cout << v << " ";
    cout << "\n";
}

signed main() {
    cin.tie(0)->sync_with_stdio(0); cin.exceptions(cin.failbit);
    int t;
    cin >> t;
    while(t--) fun();
}