#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const double PI = acos(-1.0);
const int T = 102;
int a[T], b[T];
int main() {
  ios_base::sync_with_stdio(false);
  int tc;
  cin >> tc;
  while (tc--) {
    int n;
    cin >> n;
    vector<pair<int, int> > need;
    set<int> disp;
    for (int i = 1; i <= 2 * n; i++) disp.insert(i);
    for (int i = 1; i <= n; i++) {
      cin >> b[i];
      disp.erase(b[i]);
      a[2 * i - 1] = b[i];
      need.emplace_back(2 * i, b[i]);
    }
    sort(need.begin(), need.end(), greater<pair<int, int> >());
    bool f = 0;
    while (need.size()) {
      pair<int, int> top = need.back();
      need.pop_back();
      int at = -1;
      for (auto x : disp) {
        if (x > top.second) {
          at = x;
          break;
        }
      }
      if (at == -1) {
        f = 1;
        break;
      } else {
        disp.erase(at);
        a[top.first] = at;
      }
    }
    if (f)
      cout << -1 << '\n';
    else {
      for (int i = 1; i <= 2 * n; i++) cout << a[i] << " ";
      cout << '\n';
    }
  }
  return 0;
}
