#include <bits/stdc++.h>
using namespace std;
int main() {
  bool u = 0, n = 0, z = 0;
  int a, b, c[100000] = {}, p, d, q = 1, s = 1;
  cin >> a;
  for (int i = 0; i < a; i++) {
    cin >> b;
    p = b * 2;
    s = 1;
    for (int i = 0; i <= (b * 2 - 2); i += 2) cin >> c[i];
    for (int i = 0; i <= (b * 2 - 2); i += 2) {
      u = 0;
      q = 1;
      while (1) {
        d = c[i] + q;
        if (d > p) {
          u = 1;
          break;
        } else if (p >= d) {
          n = 0;
          z = 0;
          for (int i = 0; i <= b * 2; i++)
            if (d == c[i]) {
              n = 1;
              break;
            }
          if (n == 0) {
            c[s] = d;
            s += 2;
            z = 1;
            break;
          }
          if (n == 1 && i == b * 2 - 1) {
            u = 1;
            break;
          }
        }
        q++;
      }
      if (u == 1) break;
    }
    if (u == 1)
      cout << -1 << endl;
    else {
      for (int i = 0; i < b * 2; i++) cout << c[i] << " ";
    }
    cout << endl;
    for (int i = 0; i < 10000; i++) c[i] = 0;
  }
  return 0;
}
