#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int MAXN = 1e5 + 10;
const int mod = 998244353;

struct edge {
	int v, nxt;
} e[MAXN << 1];

int head[MAXN], tot = 1;

inline 
void add(int u, int v) {
	e[++tot] = { v, head[u] }, head[u] = tot;
}

inline 
void clear(int n) {
	for (int i = 1; i <= n; i++) head[i] = 0; tot = 1;
}

int fa[MAXN];

int find(int k) {
	return k == fa[k] ? k : fa[k] = find(fa[k]);
}

inline 
bool merge(int u, int v) {
	return (u = find(u)) != (v = find(v)) && (fa[u] = v);
}

int pre[MAXN], id[MAXN];

int ans[MAXN], cnt, rt;

void init(int u) {
	if (!id[u]) rt = u;
	for (int i = head[u], v; i; i = e[i].nxt) {
		if ((i >> 1) == id[u]) continue; v = e[i].v;
		pre[v] = u, id[v] = i >> 1, init(v);
	}
}

inline 
void solve(int u) {
	for (cnt = 0; u != rt; u = pre[u]) ans[++cnt] = id[u];
}

int t, n, m, u[MAXN], v[MAXN];

int main() {
	for (scanf("%d", &t); t--; clear(n)) {
		scanf("%d%d", &n, &m), rt = 0;
		for (int i = 1; i <= m; i++) scanf("%d%d", &u[i], &v[i]);
		for (int i = 1; i <= n; i++) fa[i] = i;
		for (int i = 1; i <= m; i++) {
			if (!merge(u[i], v[i])) { init(u[i]), solve(v[i]), ans[++cnt] = i; break; }
			add(u[i], v[i]), add(v[i], u[i]);
		}
		if (!rt) { puts("-1"); continue; } sort(ans + 1, ans + cnt + 1);
		for (int i = 1; i <= cnt; i++) printf("%d ", ans[i]); puts("");
	}
}