#include <bits/stdc++.h>

using namespace std;

using ll = long long;

#define INF 0x3f3f3f3f
#define LNF (ll) 0x3f3f3f3f3f3f3f3f 

#define MOD 998244353
#define N 220

int main() {
#ifdef TEST
    freopen("zz.in", "r+", stdin);
#endif
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);    

    int t; cin >> t;
    while (t --) {
        int n; cin >> n;
        vector<ll> a(n);
        for (int i = 0; i < n; ++ i) cin >> a[i];
        vector<pair<int, int>> moves;
        bool possible = 1;
        for (int k = 60; k >= 0; -- k) {
            vector<int> s;
            for (int i = 0; i < n; ++ i) {
                if ((a[i] >> k) & 1) s.emplace_back(i);
            }
            
            if (s.empty()) continue;
            if (s.size() != 2) {
                possible = 0;
                break;
            }
            moves.emplace_back(s[0]+1, a[s[0]]);
            a[s[1]] ^= a[s[0]];
            a[s[0]] = 0;
        } 
        if (!possible) {
            cout << -1 << '\n';
        } else {
            cout << moves.size() << '\n';
            for (auto [p, x] : moves) cout << p << ' ' << x << '\n';
        }
    }
}