#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define sp " "
#define YES cout << "YES" << endl
#define NO cout << "NO" << endl
#define Yes cout << "Yes" << endl
#define No cout << "No" << endl
#define yes cout << "yes" << endl
#define no cout << "no" << endl

void messi()
{
    ll n, k;
    cin >> n >> k;
    vector<string> v(n);
    for (string &x : v)
        cin >> x;

    string ans = "";
    while (k > 0 && n > 1)
    {
        ll index = 0;
        ans = v[0] + v[1];
        for (ll i = 1; i < n - 1; i++)
        {
            string con = v[i] + v[i + 1];
            if (con > ans)
            {
                ans = con;
                index = i;
            }
        }
        v[index] = ans;
        v.erase(v.begin() + index + 1);
        n--;
        k--;
    }
    cout << ans << endl;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    ll tc = 1;
    cin >> tc;
    while (tc--)
    {
        messi();
    }
    return 0;
}