#include <bits/stdc++.h>
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast", "omit-frame-pointer", "inline")
#pragma GCC option("arch=native", "tune=native", "no-zero-upper")
#pragma GCC target( \
    "sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native,avx2")
using namespace std;
const double eps = 1E-9;
const double Exp = 2.718281828459045;
const double Pi = 3.1415926535897932;
const int Max_Bit = 63;
const int INF = 2000000000;
const long long LINF = 1000000000000000007ll;
const int MOD = 1000000007;
const int NMAX = 1000005;
const int MMAX = 505;
const int KMAX = 6;
const string CODE = "CODEFORCES";
int t[4 * NMAX];
void build(vector<int> a, int v, int tl, int tr) {
  if (tl == tr)
    t[v] = a[tl];
  else {
    int tm = (tl + tr) / 2;
    build(a, v * 2, tl, tm);
    build(a, v * 2 + 1, tm + 1, tr);
    t[v] = t[v * 2] + t[v * 2 + 1];
  }
}
int sum(int v, int tl, int tr, int l, int r) {
  if (l > r) return 0;
  if (l == tl && r == tr) return t[v];
  int tm = (tl + tr) / 2;
  return sum(v * 2, tl, tm, l, min(r, tm)) +
         sum(v * 2 + 1, tm + 1, tr, max(l, tm + 1), r);
}
long long gcd(long long a, long long b, long long& x, long long& y) {
  if (a == 0) {
    x = 0;
    y = 1;
    return b;
  }
  long long x1, y1;
  long long d = gcd(b % a, a, x1, y1);
  x = y1 - (b / a) * x1;
  y = x1;
  return d;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int T;
  for (cin >> T; T; T--) {
    int n, a[100], b[200];
    int o = 0;
    priority_queue<int> q;
    cin >> n;
    for (int i = 0; i < n; ++i) cin >> a[i];
    for (int i = 1; i <= 2 * n; ++i) {
      int fnd = 0;
      for (int j = 0; j < n; ++j)
        if (a[j] == i) fnd = j + 1;
      if (fnd == 0) {
        if (q.empty()) {
          o = 1;
          break;
        }
        int pos = -q.top();
        q.pop();
        b[pos] = i;
      } else {
        b[fnd * 2 - 2] = i;
        q.push(-fnd * 2 + 1);
      }
    }
    if (o) {
      cout << -1 << endl;
      continue;
    }
    for (int i = 0; i < 2 * n; ++i) cout << b[i] << " ";
    cout << "\n";
    ;
  }
  return 0;
}
