#include<bits/stdc++.h>
#define ll long long
#define ff first
#define ss second
#define pb push_back
using namespace std;

typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

vector<vector<int>> g;
vector<int> colors;
vector<int> marked;
vector<int> dist;


int calc(int n){
	int lo = 1, hi = 10000;
	int ans;
	while(lo <= hi){
		int mid = (lo+hi)>>1;
		if(mid * mid >= n) {
			ans = mid;
			hi = mid - 1;
		} else {
			lo = mid + 1;
		}
	}
	return ans;
}


int main() {
	ios_base::sync_with_stdio(0),cin.tie(0);
	int t; cin >> t;
	while(t--){
		g.clear();
		colors.clear();
		dist.clear();
		marked.clear();
		int n,m; cin >> n >> m;
		g.resize(n), colors.resize(n), dist.resize(n), marked.resize(n);
		for(int i = 0; i < m;++i){
			int a,b; cin >> a >> b;
			--a,--b;
			g[a].pb(b);
			g[b].pb(a);
		}

		int upTo = calc(n);
		vector<int> taken;
		int i = 0;
		while(taken.size() != upTo){
			int j = taken.size() + 1;
			taken.pb(i);
			dist[i] = 0;
			queue<int> q;
			q.push(i);
			colors[i] = j;
			while(q.size()){
				int dad = q.front(); q.pop();
				for(auto adj: g[dad]){
					if(colors[adj] != j){
						dist[adj] = dist[dad] + 1;
						colors[adj] = j;
						q.push(adj);
					}
				}
			}
			int next = i;
			for(int k = 0; k < n;++k){
				if(dist[k] <= upTo)
					marked[k] = 1;
				else if(!marked[k] && dist[k] > dist[next])
					next = k;
			}
			if(next == i) break;
			i = next;
		}

		bool posi = 1;
		for(int i = 0; i < n && posi; ++i){
			posi = marked[i] != 0;
		}

		if(posi){
			cout << taken.size() << '\n';
			for(auto va:taken)
				cout << va + 1 << ' ';
			cout << '\n';
		} else 
			cout << -1 << '\n';

	}

	return 0;
}