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

using ll=long long;
using pii=pair<int,int>;
#define sz(a) ((int)a.size())
#define all(a) a.begin(),a.end()
#define pb push_back

const int N=4005;
int n,m,dep[N],low[N],par[N],e[N][2],cnt[N],cnt2[N],cc_id[N],tl[N],tr[N],_cur,tag[N];
vector<pii> adj[N];
bool dead[N],vis[N];

void dfs(int u, int fa){
    if(vis[u]) return;
    par[u]=fa;
    dep[u]=fa==-1?0:dep[fa]+1;
    low[u]=dep[u];
    tl[u]=++_cur;
    vis[u]=1;
    for(auto [v,id]: adj[u]) if(v!=fa){
        if(vis[v]){
            low[u]=min(low[u],dep[v]);
            continue;
        }
        dfs(v,u);
        low[u]=min(low[u],low[v]);
    }
    tr[u]=_cur;
}

bool is_anc(int u, int v){
    return tl[u]<=tl[v]&&tr[u]>=tr[v];
}

void ahcorz(){
    cin >> n >> m;
    for(int i=0; i<m; ++i) dead[i]=0;
    for(int i=0,u,v; i<m; ++i){
        cin >> u >> v; u--,v--;
        e[i][0]=u,e[i][1]=v;
    }
    //cout << "de" << endl;
    vector<int> res;
    while(1){
        _cur=-1;
        for(int i=0; i<n; ++i) adj[i].clear();
        int cnt_edge=0;
        for(int i=0; i<m; ++i) if(!dead[i]){
            int u=e[i][0],v=e[i][1];
            cnt_edge++;
            adj[u].pb({v,i}),adj[v].pb({u,i});
        }
        if(cnt_edge==0) break;
        for(int i=0; i<n; ++i) vis[i]=0,par[i]=-1;
        for(int i=0; i<n; ++i){
            dfs(i,-1);
        }
        for(int i=0; i<m; ++i) cnt[i]=0;
        for(int i=0; i<n; ++i) cnt2[i]=0;
        for(int i=0; i<n; ++i){
            //cout << i << ' ' << par[i] << ' ' << dep[i] << ' ' << low[i] << "\n";
        }
        for(int i=0; i<n; ++i){
            for(auto [v,id]: adj[i]){
                if(v!=par[i]&&i!=par[v]) continue;
                if(v!=par[i]&&low[v]<dep[i]){
                    cc_id[v]=par[i];
                }
                else{
                    cc_id[v]=v;
                }
            }
            vector<pii> ch;
            for(auto [v,id]: adj[i]){
                if(par[v]==i) ch.pb({tl[v],v});
            }
            for(auto [v,id]: adj[i]){
                int tmp;
                if(!is_anc(i,v)) tmp=par[i];
                else{
                    auto it=lower_bound(all(ch),pii(tl[v],1e9));
                    it--;
                    tmp=it->second;
                }
                tag[v]=tmp;
                cnt2[cc_id[tmp]]++;
                //cout << "add " << i << ' ' << v << ' ' << tmp << ' ' << cc_id[tmp] << "\n";
            }
            int de=0;
            for(auto [v,id]: adj[i]){
                if(cnt2[v]>=2){
                    de+=cnt2[v]-1;
                }
            }
            //cout << "de " << i << ' ' << de << "\n";
            if(de==0){
                for(auto [v,id]: adj[i]) cnt[id]++;
            }
            else if(de==1){
                for(auto [v,id]: adj[i]) if(cnt2[cc_id[tag[v]]]>=2) cnt[id]++;
            }
            for(auto [v,id]: adj[i]){
                cnt2[v]=0;
            }
        }
        bool found=0;
        for(int i=0; i<m; ++i) if(cnt[i]>=2){
            res.pb(i);
            dead[i]=1;
            found=1;
        }
        if(!found){
            cout << "-1\n";
            return;
        }
    }
    reverse(all(res));
    for(auto i: res) cout << i+1 << ' ';
    cout << "\n";
}

signed main(){
    ios_base::sync_with_stdio(0),cin.tie(0);
    int t; cin >> t;
    while(t--) ahcorz();
}