#include <bits/stdc++.h>

using u32 = unsigned;
using i64 = long long;
using u64 = unsigned long long;

void solve() {
    int n;
    std::cin >> n;
    
    std::vector<i64> a(n);
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
    }
    auto olda = a;
    
    std::vector<int> u, v;
    std::vector<i64> x;
    
    std::vector<std::vector<std::pair<int, int>>> adj(n);
    for (int k = 59; k >= 0; k--) {
        std::vector<int> ones;
        std::vector<bool> vis(n);
        auto dfs = [&](auto self, int i) -> void {
            vis[i] = true;
            for (auto [j, t] : adj[i]) {
                if (vis[j]) {
                    continue;
                }
                self(self, j);
                if (a[j] >> k & 1) {
                    a[j] ^= 1LL << k;
                    a[i] ^= 1LL << k;
                    x[t] ^= 1LL << k;
                }
            }
        };
        for (int i = 0; i < n; i++) {
            if (vis[i]) {
                continue;
            }
            dfs(dfs, i);
            if (a[i] >> k & 1) {
                ones.push_back(i);
            }
        }
        if (ones.size() > 2) {
            std::cout << -1 << "\n";
            return;
        }
        if (ones.size() == 2) {
            int i = ones[0];
            int j = ones[1];
            u.push_back(i);
            v.push_back(j);
            x.push_back(1LL << k);
        }
    }
    
    a = olda;
    std::cout << u.size() << "\n";
    for (int i = 0; i < u.size(); i++) {
        assert((a[u[i]] ^ x[i]) < a[u[i]]);
        assert((a[v[i]] ^ x[i]) < a[v[i]]);
        std::cout << u[i] + 1 << " " << a[u[i]] - (a[u[i]] ^ x[i]) << "\n";
        a[u[i]] ^= x[i];
        a[v[i]] ^= x[i];
    }
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    int t;
    std::cin >> t;
    
    while (t--) {
        solve();
    }
    
    return 0;
}