#include <bits/stdc++.h>
using namespace std;
int mark[2005];
int main() {
  long long n, m, i, j, t, x, y, w, k, a, b;
  cin >> t;
  while (t--) {
    cin >> n;
    vector<pair<int, int> > v;
    memset(mark, 0, sizeof mark);
    for (i = 0; i < n; i++) {
      cin >> x;
      v.push_back({x, -1});
      mark[x] = 1;
    }
    set<int> s;
    for (i = 1; i <= 2 * n; i++) {
      if (mark[i] == 0) {
        s.insert(i);
      }
    }
    int flag = 1;
    for (i = 0; i < n; i++) {
      x = v[i].first;
      int ans = -1;
      for (auto xx : s) {
        if (xx > x) {
          ans = xx;
          break;
        }
      }
      if (ans == -1) {
        flag = -1;
        break;
      } else {
        v[i].second = ans;
        s.erase(ans);
      }
    }
    if (flag == -1) {
      cout << (-1) << "\n";
    } else {
      for (i = 0; i < n; i++) {
        cout << min(v[i].first, v[i].second) << " "
             << max(v[i].first, v[i].second) << " ";
      }
      cout << "\n";
    }
  }
  return 0;
}
