#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
const long double PI = acos(-1.0L);
const long long MOD = 1000000007LL;
template <class T>
inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
void solve() {
  int N;
  cin >> N;
  vector<int> B(N);
  for (int i = 0; i < (int)(N); ++i) cin >> B[i];
  set<int> ppp, dic;
  for (int i = 0; i < (int)(N); ++i) ppp.emplace(B[i]);
  for (int i = 0; i < (int)(2 * N); ++i)
    if (!ppp.count(i + 1)) dic.emplace(i + 1);
  vector<int> ans(2 * N);
  for (int i = 0; i < (int)(N); ++i) {
    ans[i * 2] = B[i];
    bool ok = false;
    for (auto j : dic) {
      if (j > B[i]) {
        ans[i * 2 + 1] = j;
        ok = true;
        break;
      }
    }
    if (!ok) {
      cout << -1 << '\n';
      return;
    } else
      dic.erase(ans[i * 2 + 1]);
  }
  for (int i = 0; i < (int)(2 * N); ++i) cout << ans[i] << " ";
  cout << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int Q;
  cin >> Q;
  while (Q--) {
    solve();
  }
}
