#include <bits/stdc++.h>
using namespace std;
const long long N = 200 + 10;
const long long M = 1e5 + 10;
const long long inf = 1e9 + 7;
const long long Mod = 1e9 + 7;
const double eps = 1e-6;
int T;
int n;
int a[N], b[N];
bool fix[N];
bool f;
void init() {
  for (int i = 0; i < N; ++i) {
    fix[i] = 0;
  }
  f = 1;
}
int main() {
  scanf("%d", &T);
  while (T--) {
    scanf("%d", &n);
    init();
    for (int i = 1; i <= n; ++i) {
      scanf("%d", b + i);
      a[2 * i - 1] = b[i];
      fix[b[i]] = 1;
    }
    for (int i = 2; i <= 2 * n; i += 2) {
      bool find = 0;
      for (int j = b[i / 2] + 1; j <= 2 * n; ++j) {
        if (fix[j]) continue;
        a[i] = j;
        fix[j] = 1;
        find = 1;
        break;
      }
      if (find == 0) {
        f = 0;
        break;
      }
    }
    if (f == 0)
      puts("-1");
    else {
      for (int i = 1; i <= 2 * n; ++i) printf("%d ", a[i]);
      puts("");
    }
  }
  return 0;
}
