#include <bits/stdc++.h>

using namespace std;

struct Dsu {
    vector<int> pa, rk;
    Dsu (int n) : pa(n), rk(n) {
        iota(pa.begin(), pa.end(), 0);
    }
    int anc(int x) {
        return x == pa[x] ? x : pa[x] = anc(pa[x]);
    }
    void join(int x, int y) {
        x = anc(x); y = anc(y);
        assert (x != y);
        if (rk[x] < rk[y]) swap(x, y);
        pa[y] = x;
        if (rk[x] == rk[y]) ++rk[x];
    }
};
signed main() {
    cin.tie(nullptr) -> sync_with_stdio(false);
    int T;
    cin >> T;
    while (T--) {
        int N, M;
        cin >> N >> M;
        vector<pair<int,int>> E(M);
        vector<vector<pair<int,int>>> g(N);
        for (auto &[x, y]: E)
            cin >> x >> y, --x, --y;
        Dsu dsu(N);
        vector<int> ans;
        for (int i = 0; i < M; i++) {
            auto [x, y] = E[i];
            if (dsu.anc(x) == dsu.anc(y)) {
                auto dfs = [&g, y, &ans](auto self, int i, int f) -> bool {
                    if (i == y) {
                        return true;
                    }
                    for (auto [j, eid]: g[i])
                        if (j != f) {
                            if (self(self, j, i)) {
                                ans.push_back(eid);
                                return true;
                            }
                        }
                    return false;
                };
                assert (dfs(dfs, x, -1));
                ans.push_back(i);
                break;
            } else {
                dsu.join(x, y);
                g[x].emplace_back(y, i);
                g[y].emplace_back(x, i);
            }
        }
        if (ans.empty()) {
            cout << -1 << '\n';
        } else {
            sort(ans.begin(), ans.end());
            for (int i = 0; i < ans.size(); i++)
                cout << ans[i] + 1 << (i+1==ans.size() ? '\n' : ' ');
        }
    }
}