#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;
using pii = pair<int, int>;

#define all(a) (a).begin(), (a).end()

#define int long long

void solve() {
	int n;
	cin >> n;
	vector<int> a(n);
	for (int& i : a) cin >> i;

	if (n >= 202) {
		cout << "-1\n";
		return;
	}

	set<pii, std::greater<pii>> s;
	for (int i = 0; i < n; ++i) s.insert({a[i], i});

	vector<pii> ans;

	while (!s.empty()) {
		auto ft = *s.begin();
		s.erase(ft);
		auto st = *s.begin();
		s.erase(st);

		ans.push_back(st);
		ft.first ^= st.first;

		if (s.empty()) {
			break;
		}

		auto fd = *s.begin();
		if ((fd.first & st.first) > (fd.first ^ st.first)) {
			cout << "-1\n";
			return;
		}

		if (ft.first != 0) {
			s.insert(ft);
		}
	}

	cout << ans.size() << '\n';
	for (pii i : ans) {
		cout << i.second + 1 << ' ' << i.first << '\n';
	}


}

signed main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	int t;
	cin >> t;
	while (t--) solve();


}