#include <bits/stdc++.h>

const int N = 2e5 + 10;
struct node {
    int x, y;
} ;

void solve() {
    int n, m;
    std::cin >> n >> m;
    std::vector < node > a(m);
    for(int i = 0; i < m; ++i) std::cin >> a[i].x >> a[i].y, --a[i].x, --a[i].y;
    int bl = sqrt(n);
    while(bl * bl < n) ++bl;
    std::vector < int > f(n + 3), p(n + 3), vis(n + 3);
    std::iota(f.begin(), f.end(), 0);
    for(int i = 0, cnt = 1, pos = 0; i < n; ++i, ++cnt) {
        if(cnt == bl + 1) cnt = 1, ++pos;
        p[i] = pos;
    }
    std::vector < int > ans;
    auto Get = [&](auto self, int x) -> int {
        return f[x] == x ? x : f[x] = self(self, f[x]);
    } ;
    for(int i = 0; i < m; ++i) {
        int X = Get(Get, p[a[i].x]), Y = Get(Get, p[a[i].y]);
        if(X == Y) continue;
        f[X] = Y;
        if(!vis[p[a[i].x]]) {
            vis[p[a[i].x]] = 1;
            ans.emplace_back(a[i].x);
        }
        if(!vis[p[a[i].y]]) {
            vis[p[a[i].y]] = 1;
            ans.emplace_back(a[i].y);
        }
    }
    if(ans.size() == 0) {
        ans.push_back(0);
    }
    std::cout << (int)ans.size() << '\n';
    for(auto x : ans) {
        std::cout << x + 1 << ' ';
    }
    std::cout << '\n';
}

int main() {
    std::cin.tie(nullptr) -> sync_with_stdio(false);
    int T = 1;
    std::cin >> T;
    while(T--) solve();
    return 0;
}