#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 105;
long long t, n, a[MAX_N], b;
vector<int> ans;
set<int> second;
int main() {
  cin >> t;
  while (t--) {
    cin >> n;
    second.clear();
    b = 1;
    ans.resize(2 * n + 2);
    fill(ans.begin(), ans.end(), 0);
    for (int i = 1; i <= 2 * n; ++i) {
      second.insert(i);
    }
    for (int i = 1; i <= n; ++i) {
      cin >> a[i];
      ans[2 * i - 1] = a[i];
      second.erase(a[i]);
    }
    for (int i = 1; i < 2 * n; i += 2) {
      auto it = second.lower_bound(ans[i]);
      if (it == second.end()) {
        b = false;
        break;
      }
      ans[i + 1] = *it;
      second.erase(it);
    }
    if (!b) {
      cout << -1 << endl;
      continue;
    }
    for (int i = 1; i < ans.size() - 1; ++i) {
      cout << ans[i] << " ";
    }
    cout << endl;
  }
  return 0;
}
