#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
int n;
LL a[100005], ans[65];

vector<int> hv[65];
vector<pair<int, int> > G[125];

bool vis[125];
LL dfs(int v, int p, int d) {
    vis[v] = true;
    LL ret = a[v] & (1LL << d);
    for(auto u : G[v]) if(u.first != p) {
        LL ca = dfs(u.first, v, d);
        ret ^= ca;
        ans[u.second] ^= ca;
    }
    return ret;
}
void dmerge(int d) {
    for(int i = 0; i < n; i++)
        vis[i] = false;
    for(int i = 0; i < n; i++)
        if(!vis[i] && dfs(i, -1, d)) hv[d].push_back(i);
}

void solve() {
    scanf("%d", &n);
    for(int i = 0; i < n; i++) {
        scanf("%lld", &a[i]);
    }
    if(n > 120) {
        printf("-1\n"); return;
    }

    for(int i = 0; i < n; i++) G[i].clear();
    for(int i = 59; i >= 0; i--) {
        hv[i].clear();
        dmerge(i);
        if(hv[i].size() == 0) continue;
        if(hv[i].size() == 2) {
            int u = hv[i][0], v = hv[i][1];
            G[u].push_back(make_pair(v, i));
            G[v].push_back(make_pair(u, i));
            ans[i] = 1LL << i;
            continue;
        }
        printf("-1\n"); return;
    }

    vector<pair<int, LL> > ret;
    for(int i = 59; i >= 0; i--) if(hv[i].size() == 2) {
        int u = hv[i][0], v = hv[i][1];
        ret.push_back(make_pair(u, a[u] - (a[u] ^ ans[i])));
        a[u] ^= ans[i]; a[v] ^= ans[i];
    }
    printf("%d\n", (int)ret.size());
    for(int i = 0; i < n; i++) printf("%d %lld\n", ret[i].first + 1, ret[i].second);
}

int main() {
    int T;
    scanf("%d", &T);
    while(T--) solve();
    return 0;
}