// #pragma comment(linker, "/STACK:102400000,102400000")
#pragma GCC optimize("O3")
#pragma GCC optimize("O2")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
// #pragma GCC optimize("trapv")
#include<bits/stdc++.h>
// #include <bits/extc++.h>
#define int long long
// #define double long double
// #define i128 long long
// #define double long double
using namespace std;
 
#define rep(i,n) for (int i=0;i<(int)(n);++i)
#define rep1(i,n) for (int i=1;i<=(int)(n);++i)
#define range(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define pb push_back
#define F first
#define S second
 
typedef long long ll;
typedef unsigned long long ull;
// typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;
 
int dx[]={1,-1,0,0};
int dy[]={0,0,1,-1};
const int mod=1e9+7;
const double EPS=1e-9;
// const double pi=acos(-1);
const int INF=1e18;
const int N=500007;
mt19937 rng(1235);

int n,m,par[N],f[N],fid[N];
bool vis[N];
vector<pii> g[N];
int fnd(int u){
    if (par[u]==u) return u;
    return par[u]=fnd(par[u]);
}
int unite(int u,int v){
    int pu=fnd(u), pv=fnd(v);
    if (pu==pv) return 1;
    par[pu]=pv; return 0;
}

int x,y;
void dfs(int u,int p){
    for (auto c:g[u]){
        if (c.F==p) continue;
        f[c.F]=u, fid[c.F]=c.S;
        dfs(c.F,u);
    }

}
signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    cout.precision(15);
    int _;
    cin>>_;
    while (_--){
        cin>>n>>m;
        x=-1, y=-1;
        rep1(i,n) par[i]=i, g[i].clear(),f[i]=-1,vis[i]=0;
        vector<pii> edges(m);
        for (auto &c:edges) cin>>c.F>>c.S;
        int idx=1;
        for (auto c:edges){
            if (unite(c.F,c.S)) {
                x=c.F, y=c.S;
                dfs(c.F,-1);
                break;
            }
            g[c.F].pb({c.S,idx}), g[c.S].pb({c.F,idx});
            idx++;
        }
        if (x==-1){
            cout<<-1<<"\n";
        }
        else{
            vi ans;
            ans.pb(idx);
            while (x!=y) {
                ans.pb(fid[y]), y=f[y];
            }
            sort(range(ans));
            cout<<ans[0];
            rep1(i,sz(ans)-1) cout<<" "<<ans[i];
            cout<<"\n";
        }
        
    }
    return 0;
}
/*

*/