#include <bits/stdc++.h>
using namespace std;
int n, a, m, x;
bool dziala;
bitset <201> s;
vector<int> v;
int main()
{
    cin >> n;
    for (int j = 1; j <= n; j++)
    {
        s.reset();
        v.clear();
        dziala = 0;
        cin >> m;
        for (int i = 1; i <= m; i++)
        {
            cin >> a;
            s[a] = true;
            v.push_back(a);
            x = a + 1;
            while (x < m * 2)
            {
                if (s[x] == 1)
                    x++;
                else
                {
                    s[x] = true;
                    v.push_back(x);
                    break;
                }
            }
            if (x > m * 2)
            {
                cout << -1;
                dziala = 1;
                break;
            }

        }
        if (dziala == 0)
        {
            for (int i = 0; i < v.size(); i++)
                cout << v[i] << " ";
        }
        cout << endl;
    }
}