#include <bits/stdc++.h>   using namespace std;   signed main() {     ios::sync_with_stdio(false);     cin.tie(0);     int t;     cin >> t;     auto solve = []() {       int n;       cin >> n;       vector<pair<int, int>> a(n);       for (int i = 0; i < n; i++) {         cin >> a[i].first;         a[i].first--;       }       vector<int> ans(n + n);       vector<int> used(n + n);       for (int i = 0; i < n; i++) {         ans[i * 2] = a[i].first;         a[i].second = i * 2;         used[a[i].first] = 1;       }       for (int i = 1; i < n + n; i += 2) {         int x = ans[i - 1];         int j;         for (j = x + 1; j < n + n && used[j]; j++)           ;         if (j == n + n) {           cout << -1 <<   n ;           return 0;         }         used[j] = 1;         ans[i] = j;       }       for (int i = 0; i < n + n; i++) {         if (i > 0) cout <<    ;         cout << ans[i] + 1;       }       cout <<   n ;     };     while (t--) solve();     return 0;   }   