#include <bits/stdc++.h>
using namespace std;
int f(map<int, int> &mp, int b[], int n, int l) {
  bool x = 0;
  for (int j = l + 1; j <= 2 * n; j++) {
    if (!mp[j]) {
      mp[j] = 1;
      x = 1;
      return j;
    }
  }
  return 0;
}
int main() {
  int T;
  cin >> T;
  while (T--) {
    int n;
    cin >> n;
    int a[n + 3], b[2 * n + 5];
    map<int, int> mp;
    for (int i = 1; i <= n; i++) cin >> a[i], mp[a[i]]++;
    bool y = 0;
    int x = 1;
    for (int i = 1; i <= 2 * n; i += 2, x++) {
      int k = f(mp, b, n, a[x]);
      if (!k) {
        y = 1;
        break;
      }
      b[i + 1] = k;
      b[i] = a[x];
    }
    if (y) {
      cout << "-1\n";
      continue;
    }
    x = 1;
    for (int i = 1; i <= 2 * n; i += 2, x++) {
      if (a[x] == min(b[i], b[i + 1])) continue;
      cout << "-1\n";
      y = 1;
      break;
    }
    if (!y) {
      for (int i = 1; i <= 2 * n; i++) cout << b[i] << " \n"[i == 2 * n];
    }
  }
}
