#include<bits/stdc++.h>
using namespace std;
using pii=pair<int,int>;
using vp=vector<pii>;
using vi=vector<int>;
const int N=4005;
int n,m;vp edge[N];
bool vs[N],tg[N];
int dg[N];vi rs;
int dfn[N],low[N],cnt;
int st[N],tp,bel[N],tot;
void tarjan(int u,int ls)
{
    //cout<<"TJ:"<<u<<' '<<ls<<'\n';
    dfn[u]=low[u]=++cnt;
    st[++tp]=u;
    for(auto [v,id]:edge[u])
    {
        if(vs[id]||!tg[v]||id==ls)continue;
        if(!dfn[v])tarjan(v,id),low[u]=min(low[u],low[v]);
        else low[u]=min(low[u],dfn[v]);
    }if(dfn[u]==low[u])
    {
        bel[u]=++tot;
        while(st[tp]^u)
        bel[st[tp--]]=tot;
        tp--;
    }
}bool flag;
void solve(vi vc)
{
    if(flag)return;vi cr;
    if(vc.size()<=1)return;
    for(int u:vc)tg[u]=1,dfn[u]=0;
    cnt=tot=0;for(int u:vc)
    if(!dfn[u])tarjan(u,0);
    vector<vi> S(tot+1);
    for(int u:vc)dg[u]=0,
    S[bel[u]].push_back(u);
    for(int u:vc)
    for(auto [v,id]:edge[u])
    {
        if(vs[id]||!tg[v])continue;
        if(bel[u]^bel[v])
        vs[id]=1,rs.push_back(id);
        else dg[u]++;
    }for(int u:vc)tg[u]=0;
    for(int i=1;i<=tot;i++)
    {
        if(S[i].size()==1)continue;
        for(int u:S[i])tg[u]=1;
        bool fl=0;for(int u:S[i])
        for(auto [v,id]:edge[u])
        {
            if(fl||vs[id]||!tg[v])continue;
            if(dg[u]==2&&dg[v]==2)
            cr.push_back(id),
            vs[id]=1,fl=1;
        }for(int u:S[i])tg[u]=0;
        if(!fl)return flag=1,void();
    }for(int i=1;i<S.size();i++)solve(S[i]);
    for(int id:cr)rs.push_back(id);
}
void solve()
{
    cin>>n>>m;rs.clear();
    for(int i=1;i<=n;i++)
    edge[i].clear();
    fill(vs+1,vs+m+1,0);
    for(int i=1;i<=m;i++)
    {
        int x,y;cin>>x>>y;
        edge[x].push_back({y,i});
        edge[y].push_back({x,i});
    }vi vc;for(int i=1;i<=n;i++)
    vc.push_back(i);flag=0;solve(vc);
    if(flag)return cout<<"-1\n",void();
    for(int c:rs)cout<<c<<' ';cout<<'\n';
}
int main()
{
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int t;cin>>t;while(t--)solve();return 0;
}