#include <bits/stdc++.h>   using namespace std;   int mpow(int base, int exp);   void solve() {     long long int n;     cin >> n;     vector<long long int> v(n);     vector<long long int> cnt(2 * n + 1, 0);     for (long long int i = 0; i < (n); i++) {       cin >> v[i];       cnt[v[i]]++;     }     vector<long long int> out;     for (long long int i = 0; i < (n); i++) {       out.push_back(v[i]);       bool flag = true;       for (long long int j = v[i] + 1; j <= 2 * n; j++) {         if (cnt[j] == 0) {           out.push_back(j);           cnt[j]++;           flag = false;           break;         }       }       if (flag) {         cout << -1 <<   n ;         return;       }     }     for (auto i : out) cout << i <<    ;     cout <<   n ;     ;   }   int main() {     int t;     cin >> t;     while (t--) solve();     return 0;   }   int mpow(int base, int exp) {     base %= 1000000007;     int result = 1;     while (exp > 0) {       if (exp & 1) result = ((long long int)result * base) % 1000000007;       base = ((long long int)base * base) % 1000000007;       exp >>= 1;     }     return result;   }   