#include <bits/stdc++.h>
using namespace std;
int main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n, i, p = 0, q, h, r = 0, j;
    cin >> n;
    long long a[n], b[2 * n], c[2 * n];
    memset(c, 0, sizeof(c));
    for (i = 0; i < n; i++) {
      cin >> a[i];
    }
    for (i = 0; i < n; i++) {
      c[a[i] - 1] = 1;
    }
    for (i = 0; i < n; i++) {
      h = 1;
      b[2 * i] = a[i];
      for (j = a[i]; j < 2 * n; j++) {
        if (c[j] != 1) {
          break;
        }
      }
      b[2 * i + 1] = j + 1;
      if (j < 2 * n) c[j] = 1;
    }
    for (i = 0; i < 2 * n; i++) {
      if (b[i] <= 2 * n) c[b[i] - 1] = 1;
    }
    for (i = 0; i < 2 * n; i++) {
      if (c[i] == 0) {
        r = 1;
        break;
      }
    }
    if (r == 1) {
      cout << "-1" << endl;
    } else {
      for (i = 0; i < 2 * n; i++) {
        cout << b[i] << " ";
      }
      cout << endl;
    }
  }
}
