#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;
#define MOD 998244353
#define pb push_back
#define mp make_pair
typedef long long int LLI;
typedef vector<int> vi;

LLI a[100000];
int main() {
    int i;
    int t,n;
    scanf("%d",&t);
    while (t--) {
        scanf("%d",&n);
        for (i = 0; i < n; i++) scanf("%lld",&a[i]);
        if (n > 200) printf("-1\n");
        else {
            vector<pii> ans;
            while (1) {
                int m = max_element(a,a+n)-a;
                if (a[m] == 0) {
                    printf("%d\n",ans.size());
                    for (pii p: ans) printf("%d %d\n",p.first+1,p.second);
                    break;
                }
                vi poss;
                for (i = 0; i < n; i++) {
                    if ((i != m) && ((a[i]^a[m]) < a[i])) poss.pb(i);
                }
                if ((poss.size() != 1) || (ans.size() == 100)) {
                    printf("-1\n");
                    break;
                }
                else {
                    ans.pb(mp(m,a[m]));
                    a[poss[0]] ^= a[m];
                    a[m] = 0;
                }
            }
        }
    }

    return 0;
}