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

const int LOG = 61;

void solve() {
    int n;
    cin >> n;
    vector<long long> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }

    vector<pair<int, int>> ops;
    bool possible = true;
    for (int i = LOG - 1; i >= 0; i--) {
        vector<int> inds;
        for (int j = 0; j < n; j++) {
            if (a[j] & (1ll << i)) {
                inds.push_back(j);
            }
        }
        if (inds.empty()) {
            continue;
        }
        if (inds.size() > 2) {
            possible = false;
            break;
        }
        a[inds[1]] ^= a[inds[0]];
        ops.emplace_back(inds[0] + 1, a[inds[0]]);
        a[inds[0]] = 0;
    }
    
    if (possible) {
        cout << ops.size() << "\n";
        for (auto [ind, rem] : ops) {
            cout << ind << " " << rem << "\n";
        }
    } else {
        cout << "-1\n";
    }
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

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