#include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int t;     cin >> t;     while (t--) {       int n;       cin >> n;       int b[n];       int ans[2 * n];       for (long long i = 0; i < n; i++) cin >> b[i];       set<int> a;       for (long long i = 0; i < 2 * n; i++) a.insert(i + 1);       for (long long i = 0; i < n; i++) {         ans[2 * i] = b[i];         a.erase(b[i]);       }       bool poss = true;       for (long long i = 0; i < n; i++) {         set<int>::iterator up = upper_bound(a.begin(), a.end(), b[i]);         if (up != a.end()) {           ans[2 * i + 1] = *up;           a.erase(up);         } else {           cout << -1 <<   n ;           poss = false;           break;         }       }       if (poss) {         for (long long i = 0; i < 2 * n - 1; i++) cout << ans[i] <<    ;         cout << ans[2 * n - 1] <<   n ;       }     }     return 0;   }   