#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int ans = 0, sign = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') sign = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    ans = ans * 10 + (ch - '0');
    ch = getchar();
  }
  return ans * sign;
}
const double PI = acos(-1.0);
const int mod = 1e9 + 7;
const int N = 100 + 5;
int a[N], b[N + N];
int vis[N + N];
void solve() {
  int n = read();
  bool flag = true;
  for (int i = 1; i <= n; i++) {
    a[i] = read();
  }
  memset(b, 0, sizeof(b));
  memset(vis, 0, sizeof(vis));
  for (int i = 1; i <= n; i++) {
    b[i * 2 - 1] = a[i];
    vis[a[i]] = 1;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = a[i] + 1; j <= 2 * n; j++)
      if (!vis[j] && j > a[i]) {
        b[i * 2] = j;
        vis[j] = 1;
        break;
      }
    if (!b[i * 2]) {
      flag = false;
      break;
    }
  }
  if (!flag)
    cout << "-1" << endl;
  else {
    for (int i = 1; i <= 2 * n - 1; i++) {
      cout << b[i] << " ";
    }
    cout << b[2 * n] << endl;
  }
}
int main() {
  int t = read();
  while (t--) {
    solve();
  }
  return 0;
}
