#include<stdio.h>

#include<string.h>

#include<math.h>

#include<algorithm>

using namespace std;

const int maxn = ;

int c[maxn][maxn];

int father[maxn];

int flag[maxn];

struct abc{

    int fei, a, b;

}dt[maxn*maxn];

struct ans{

    int aa, bb;

}anss[maxn*maxn];

bool cmp(const abc&a, const abc&b)

{

    if (a.fei == b.fei&&a.a == b.a) return a.b < b.b;

    if (a.fei == b.fei) return a.a < b.a;

    return a.fei < b.fei;

}

bool cmp2(const ans&a, const ans&b)

{

    if (a.aa == b.aa) return a.bb < b.bb;

    return a.aa < b.aa;

}

int find(int x)

{

    if (x != father[x]) father[x] = find(father[x]);

    return father[x];

}

int main()

{

    int sb;

    scanf("%d", &sb);

    while (sb--)

    {

        int n, i, j;

        scanf("%d", &n);

        memset(c, , sizeof(c));

        memset(father, , sizeof(father));

        memset(flag, , sizeof(flag));

        int q = ;

        for (i = ; i <= ; i++) father[i] = i;

        for (i = ; i <= n; i++) for (j = ; j <= n; j++) scanf("%d", &c[i][j]);

        for (i = ; i <= n; i++)

        {

            for (j = i + ; j <= n; j++)

            {

                if (c[i][j] != )

                {

                    dt[q].a = i;

                    dt[q].b = j;

                    dt[q].fei = c[i][j];

                    q++;

                }

            }

        }

        sort(dt, dt + q, cmp);

        int qq = ;

        for (i = ; i < q; i++)

        {

            int x = find(dt[i].a);

            int y = find(dt[i].b);

            if (x != y)

            {

                father[x] = y;

                anss[qq].aa = dt[i].a;

                anss[qq].bb = dt[i].b;

                qq++;

            }

        }

        for (i = ; i <= n; i++){int u = find(i);flag[u]++;}

        int dd = ;

        for (i = ; i <= n; i++){if (flag[i] >  && flag[i] == n){dd = ;break;}}

        if (dd==)

        {

            sort(anss, anss + qq, cmp2);

            for (i = ; i < qq; i++)

            {

                if (i < qq-)printf("%d %d ", anss[i].aa, anss[i].bb);

                else printf("%d %d\n", anss[i].aa, anss[i].bb);

            }

        }

        else if (dd == ) printf("-1\n");

    }

    return ;

}