#include <bits/stdc++.h>
using namespace std;
const int N = 105;
int T, n, tot;
int a[N], b[N << 1];
bool vis[N << 1];
int main() {
  scanf("%d", &T);
  while (T--) {
    memset(vis, false, sizeof(vis));
    scanf("%d", &n);
    for (register int i = 1; i <= n; ++i) scanf("%d", &a[i]), vis[a[i]] = true;
    bool jay = true;
    for (register int i = 1; i <= n; ++i)
      if (a[i] == 2 * n) {
        jay = false;
        break;
      }
    if (!jay) {
      puts("-1");
      continue;
    }
    int tot = 0;
    for (register int i = 1; i <= n; ++i) {
      bool flag = false;
      for (register int j = a[i] + 1; j <= 2 * n; ++j)
        if (!vis[j]) {
          b[++tot] = a[i];
          b[++tot] = j;
          vis[a[i]] = vis[j] = true;
          flag = true;
          break;
        }
      if (!flag) {
        jay = false;
        break;
      }
    }
    if (!jay) {
      puts("-1");
      continue;
    }
    for (register int i = 1; i <= tot; ++i) printf("%d ", b[i]);
    puts("");
  }
  return 0;
}
