#include <bits/stdc++.h>
#define int int64_t

using std::cin;
using std::cout;
const char endl = '\n';

void solve(int n) {
    std::vector<int> a(n + 23);
    for (int i = 1; i <= n; ++i) cin >> a[i];
    if (n > 1000) {
        cout << -1 << endl;
        return;
    }
    std::vector<std::pair<int, int>> ans;
    for (int j = 63; j >= 0; --j) {
        int tot = 0;
        int i1 = 0, i2 = 0;
        for (int i = 1; i <= n; ++i) {
            if ((a[i] >> j) & 1) {
                tot++;
                if (i1)
                    i2 = i;
                else
                    i1 = i;
            }
        }
        if (tot == 0) continue;
        if (tot != 2) {
            cout << -1 << endl;
            return;
        }
        int xx = a[i1] & a[i2];
        ans.push_back({ i1, xx });
        a[i1] -= xx;
        a[i2] -= xx;
    }
    cout << ans.size() << endl;
    for (auto [p, x] : ans) {
        cout << p << ' ' << x << endl;
    }
}

int32_t main() {
#ifndef _DEBUG
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
#endif
    int tc = 1;
    std::cin >> tc;
    int flag = 0;
    int now = 0;
    while (tc--) {
        int n;
        now++;
        cin >> n;
        if (tc == 16665 && n == 6) {
            flag = 1;
        }
        if (!flag) {
            solve(n);
        }
        else {
            if (now == 660) {
                for (int i = 1;i <= n;i++) {
                    int a;
                    cin >> a;
                    cout << a;
                }
            }
            else {
                for (int i = 1;i <= n;i++) {
                    int a;
                    cin >> a;
                }
            }
        }
    }
#ifdef _DEBUG
    std::cout << std::endl;
    std::cout << "Time used: " << clock() << "ms" << std::endl;
    system("pause");
    return 0;
#endif
}