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

using ll = long long;
using ld = long double;

#define all(a) begin(a), end(a)
#define len(a) int((a).size())

void solve(int /* test_num */) {
    int n;
    cin >> n;

    constexpr int LG = 61;
    array<vector<int>, LG> for_bit;
    vector<ll> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        for_bit[__lg(a[i])].push_back(i);
    }

    vector<pair<int, ll>> ops;
    for (int bit = LG - 1; bit >= 0; bit--) {
        assert(len(for_bit[bit]) % 2 == 0);
        if (for_bit[bit].empty()) {
            continue;
        }
        if (len(for_bit[bit]) > 2) {
            cout << "-1\n";
            return;
        }

        ll x = (a[for_bit[bit][0]] ^ a[for_bit[bit][1]]);
        ops.emplace_back(for_bit[bit][0], a[for_bit[bit][0]]);
        if (x > 0) {
            a[for_bit[bit][1]] = x;
            for_bit[__lg(x)].push_back(for_bit[bit][1]);
        }
    }

    assert(len(ops) <= 100);
    cout << len(ops) << '\n';
    for (auto [i, d] : ops) {
        cout << i + 1 << ' ' << d << '\n';
    }
}

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    int tests;
    cin >> tests;
    for (int test_num = 1; test_num <= tests; test_num++) {
        solve(test_num);
    }
}