#include <bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
typedef long long ull;
typedef unsigned long long uull;
typedef pair<int, int> PII;
typedef pair<int,PII> PIII;
typedef __int128 lll;
mt19937 rnd1(random_device{}());
mt19937_64 rnd2(random_device{}());
// uniform_int_depthtribution<int> deptht1(0,2e18);    //定义deptht1为0——100的随机整数
// uniform_real_depthtribution<double> deptht2(-10,10);    //定义deptht2为-10——10的随机浮点数
//#define mp make_pair
//fflush(stdout);
inline void print(__int128 x){//输出模板 
    if(x<0){
        putchar('-');
        x=-x;
    }
    if(x>9) print(x/10);
    putchar(x%10+'0');
}
inline int read()
{
    int X = 0;
    bool flag = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9')
    {
        if (ch == '-')
            flag = 0;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9')
    {
        X = (X << 1) + (X << 3) + ch - '0';
        ch = getchar();
    }
    if (flag)
        return X;
    return ~(X - 1);
}
const ull mod = 998244353,INF = 2e18;
ull qpow(ull a, ull b)
{
    ull res = 1;
    a %= mod;
    assert(b >= 0);
    for (; b; b >>= 1)
    {
        if (b & 1)
            res = res * a % mod;
        a = a * a % mod;
    }
    return res;
}
inline int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
inline int lcm(int a, int b) { return a / gcd(a, b) * b; }
const int N = 100010,M = 200100;

int a[N];
int cnt[110];
vector<int> p[110];

void solve()
{
    int n;
    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i];
    for(int j=0;j<=59;j++) cnt[j] = 0,p[j].clear();
    int c = 0;
    for(int i=1;i<=n;i++)
        for(int j=0;j<=59;j++)
            if((a[i]>>j)&1)
            {
                cnt[j]++;
                if(cnt[j]>2) 
                {
                    cout<<-1<<'\n';
                    return;
                }
                p[j].push_back(i);
            }
    for(int i=0;i<=59;i++) 
        if(cnt[i]&1)
        {
            cout<<-1<<'\n';
            return;
        }
        else if(cnt[i]) c++;
    cout<<c<<'\n';
    for(int i=0;i<=59;i++)
        if(cnt[i])
        {
            cout<<p[i][0]<<' '<<(1ll<<i)<<'\n';
        }
    
}   

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