#include<bits/stdc++.h>
#define ll    long long

template<typename T, typename = void>
struct is_printable : std::false_type {};

template<typename T>
struct is_printable<T, std::void_t<decltype(std::declval<std::ostream&>() << std::declval<T>())>> : std::true_type {};
template <typename T>
void print(const std::pair<T, T>& pair) {
    std::cout << "(" << pair.first << ", " << pair.second << ")";
}

// General print function
template <typename T>
void print(const T& val) {
    std::cout << val;
}

// Print function for std::vector
template <typename T>
void print(const std::vector<T>& vec) {
    std::cout << '[';
    int n = vec.size();
    for (int i = 0; i < n; i++) {
        print(vec[i]);
        if (i < n - 1) {
            std::cout << ",";
        }
    }
    std::cout << ']' << '\n';
}

// Variadic template print function
template<typename T, typename... Args>
void print(const T& t, const Args&... args) {
    print(t);
    std::cout << (is_printable<T>::value ? ' ' : '\0');
    print(args...);
    if (sizeof...(args) == 1 && is_printable<T>::value) std::cout << '\n';

}

inline unsigned count_bits(uint64_t v) {
  v = (v & 0x5555555555555555) + ((v >> 1) & 0x5555555555555555);
  v = (v & 0x3333333333333333) + ((v >> 2) & 0x3333333333333333);
  v = (v & 0x0f0f0f0f0f0f0f0f) + ((v >> 4) & 0x0f0f0f0f0f0f0f0f);
  v = (v & 0x00ff00ff00ff00ff) + ((v >> 8) & 0x00ff00ff00ff00ff);
  v = (v & 0x0000ffff0000ffff) + ((v >> 16) & 0x0000ffff0000ffff);
  v = (v & 0x00000000ffffffff) + ((v >> 32) & 0x00000000ffffffff);
  return v;
}

void solve(){
    int n;
    std::cin >> n;
    std::vector<ll> a(n), tmp;
    ll sum = 0;
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
        sum += count_bits(a[i]);
    }
    std::vector<std::pair<ll, ll>> ans;
    for (ll d = 60; d >= 0; d--) {
        tmp.clear();
        for (int i = 0; i < n; i++) {
            if ((a[i] >> d) & 1) {
                tmp.push_back(i);
            }
        }
        if (tmp.size() == 2) {
            ans.push_back({tmp[0] + 1, a[tmp[0]]});
            a[tmp[1]] ^= a[tmp[0]];
            a[tmp[0]] = 0;
        }
    }
    if (ans.empty()) {
        std::cout << "-1\n";
    }
    else {
        std::cout << ans.size() << std::endl;
        for (auto& [x, y] : ans) {
            std::cout << x << " " << y << "\n";
        }
        if (std::any_of(a.begin(), a.end(), [&](int i){return a[i];})) {
            std::cout << "-1\n";
        }
    }


    

}
int main(){
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int t = 1;
    std::cin >> t;
    while (t--) solve();
    return 0;
}