#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 500;
const long long mod = 1e9 + 7;
const long long cmod = 998244353;
const long long inf = 1LL << 61;
const int M = 1e6 + 500;
const long long int ths = 1LL << 40;
const int NN = 5e3 + 6;
void solve() {
  long long int n;
  cin >> n;
  long long int b[n + 1], a[2 * n + 1];
  set<long long int> s;
  for (int i = 1; i <= 2 * n; i++) s.insert(i);
  for (int i = 1; i <= n; i++) {
    cin >> b[i];
    s.erase(b[i]);
  }
  vector<long long int> v;
  for (auto it : s) v.push_back(it);
  long long int idx = 1;
  bool ok = 1;
  for (int i = 1; i <= n; i++) {
    a[idx] = b[i];
    idx++;
    long long int x = *s.upper_bound(b[i]);
    if (s.count(x) == 0) {
      ok = 0;
      break;
    }
    s.erase(x);
    a[idx] = x;
    idx++;
  }
  if (!ok) {
    cout << -1;
  } else {
    for (int i = 1; i <= 2 * n; i++) cout << a[i] << ' ';
  }
  cout << '\n';
  return;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
