#include <bits/stdc++.h>
using namespace std;
const long long int mod = 1e9 + 7;
const double pie = 3.14159265358979323846;
const char nl = '\n';
const char spc = ' ';
template <typename Type>
istream &operator>>(istream &in, vector<Type> &v) {
  long long int n = v.size();
  for (int i = 0; i < n; i++) in >> v[i];
  return in;
}
template <typename Type>
ostream &operator<<(ostream &out, vector<Type> &v) {
  for (auto value : v) out << value << ' ';
  out << nl;
  return out;
}
bool isPrime(long long int n) {
  if (n < 4) return true;
  if (n % 2 == 0) return false;
  long long int i = 3;
  while (i * i <= n) {
    if (n % i == 0) return false;
    i += 2;
  }
  return true;
}
void solve() {
  long long int n;
  cin >> n;
  vector<long long int> b(n);
  vector<long long int> cnt(300, 0);
  for (long long int i = 0; i < n; ++i) {
    cin >> b[i];
    cnt[b[i]] = 1;
  }
  vector<long long int> a;
  for (long long int i = 0; i < n; ++i) {
    a.emplace_back(b[i]);
    long long int k = b[i] + 1;
    while (cnt[k]) ++k;
    a.emplace_back(k);
    cnt[b[i]] = cnt[k] = 1;
  }
  for (long long int i = 1; i <= 2 * n; ++i) {
    if (cnt[i] != 1) {
      cout << "-1" << nl;
      return;
    }
  }
  cout << a;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int t;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
