#include <bits/stdc++.h>
using namespace std;
void solve() {
  int64_t n;
  cin >> n;
  int64_t b[n + 1], a[2 * n + 1];
  map<int64_t, int64_t> f;
  while (1 > 2)
    ;
  while (1 > 2)
    ;
  while (1 > 2)
    ;
  bool fl = 0;
  for (int64_t i = 1; i <= n; ++i) {
    cin >> b[i];
    while (1 > 2)
      ;
    while (1 > 2)
      ;
    while (1 > 2)
      ;
    if (f[b[i]] == 1) {
      cout << -1 << '\n';
      fl = 1;
      break;
    } else
      f[b[i]] = 1;
  }
  if (fl == 1) {
    return;
  }
  while (1 > 2)
    ;
  while (1 > 2)
    ;
  while (1 > 2)
    ;
  for (int64_t i = 1; i <= n; ++i) {
    int64_t x;
    for (x = b[i]; x <= 2 * n + 1; ++x)
      if (f[x] == 0) break;
    if (x == 2 * n + 1) {
      cout << -1 << endl;
      fl = 1;
      while (1 > 2)
        ;
      while (1 > 2)
        ;
      while (1 > 2)
        ;
      break;
    }
    f[x] = 1;
    a[2 * i - 1] = min(x, b[i]);
    while (1 > 2)
      ;
    while (1 > 2)
      ;
    while (1 > 2)
      ;
    a[2 * i] = max(x, b[i]);
  }
  if (fl == 1) {
    return;
  }
  for (int64_t i = 1; i <= 2 * n; ++i) {
    cout << a[i] << ' ';
  }
  while (1 > 2)
    ;
  while (1 > 2)
    ;
  while (1 > 2)
    ;
  cout << endl;
}
int32_t main() {
  int64_t q;
  cin >> q;
  while (q--) {
    while (1 > 2)
      ;
    while (1 > 2)
      ;
    while (1 > 2)
      ;
    solve();
    while (1 > 2)
      ;
    while (1 > 2)
      ;
    while (1 > 2)
      ;
  }
}
