#include <iostream>
    #include <vector>
    #include <set>
    #include <cmath>
    #include <algorithm>
    #include <string>

    using namespace std;

    #define fastInp ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    typedef long long ll;
    typedef long double ld;

    const ll SIZE = 5 * 1e5, MOD = 1e9 + 7;
    ll n, m, q;
    vector<ll> vec;

    int main() {
        fastInp;

        cin >> q;

        while (q--) {
            ll n;
            cin >> n;

            vec.resize(n);
            vector<ll> ans;
            vector<bool> used;
            used.resize(n * 2 + 2);
            ans.resize(n * 2);
            bool flag = false;
            for (int i = 0; i < n; i++) {
                cin >> vec[i];
                if (used[vec[i]]) flag = true;
                used[vec[i]] = true;
                ans[i * 2] = vec[i];
            }


            for (int i = 0; i < n * 2; i++) {
                if (i % 2 != 0) {
                    ll ind = ans[i - 1];
                    while (used[ind]) {
                        ind++;
                    }
                    if (ind == n * 2 + 1) {
                        flag = true;
                    }
                    else {
                        used[ind] = true;
                        ans[i] = ind;
                    }
                }
            }
            if (flag) {
                cout << "-1\n";
            }
            else {
                for (int i = 0; i < ans.size(); i++) cout << ans[i] << " ";
                cout << "\n";
            }
        }

        return 0;
    }