#include<cstdio>
#include<iostream>
#include<vector>
#include<algorithm>
#define RI register int
#define CI const int&
using namespace std;
typedef pair <int,int> pi;
const int N=100005;
int t,n,m,x,y,fa[N],pre[N],lst[N]; vector <pi> v[N]; vector <int> ans;
inline int getfa(CI x)
{
	return fa[x]!=x?fa[x]=getfa(fa[x]):x;
}
inline void DFS(CI now,CI st,CI tar)
{
	if (now==tar)
	{
		for (int x=tar;x!=st;x=pre[x]) ans.push_back(lst[x]); return;
	}
	for (auto [to,id]:v[now]) if (!~pre[to]) pre[to]=now,lst[to]=id,DFS(to,st,tar);
}
int main()
{
	//freopen("K.in","r",stdin); freopen("K.out","w",stdout);
	for (scanf("%d",&t);t;--t)
	{
		RI i; for (scanf("%d%d",&n,&m),i=1;i<=n;++i) pre[i]=-1,fa[i]=i,v[i].clear();
		bool flag=0; for (i=1;i<=m;++i)
		{
			if (scanf("%d%d",&x,&y),flag) continue;
			if (getfa(x)!=getfa(y))	fa[getfa(x)]=getfa(y),v[x].push_back(pi(y,i)),v[y].push_back(pi(x,i));
			else
			{
				flag=1; ans.clear(); pre[x]=0; DFS(x,x,y);
				ans.push_back(i); sort(ans.begin(),ans.end());
				for (RI j=0;j<ans.size();++j) printf("%d%c",ans[j]," \n"[j==ans.size()-1]);
			}
		}
		if (!flag) puts("-1");
	}
}