#include <bits/stdc++.h>
using namespace std;
#define SC scanf
#define PF printf
#define ull unsigned long long
#define ld long double
#define F first
#define S second
#define pb push_back
#define sort_a(a) sort(a.begin(),a.end());
#define sort_d(a) sort(a.rbegin(),a.rend());
#define READ(f) freopen(f, "r", stdin)
#define WRITE(f) freopen(f, "w", stdout)
#define rev(s) reverse(s.begin(),s.end())
#define P(ok) cout << (ok ? "YES\n": "NO\n")
#define __Heart__ ios_base :: sync_with_stdio(false); cin.tie(NULL);
#define ll long long
typedef pair< ll , ll> PII;
void solve()
{
int n , k; cin >> n >> k ;
vector < string > v(n) ;
for(auto &x : v) cin >> x ;
while(k-- && v.size() > 1){
string bestAd = "" ;
int pos = -1 ;
for(int i = 0 ; i < v.size() - 1 ; i++){
string cur = v[i] + v[i + 1] ;
if(cur > bestAd || pos == -1){
bestAd = cur ;
pos = i ;
}
}
// cout << pos << " " << bestAd << endl ;
if(pos != -1){
v[pos] = bestAd ;
v.erase(v.begin() + pos + 1) ;
bestAd = "" ;
}
// cout << "printing array.... " << endl ;
// for(auto it : v) cout << it << " " ; cout << endl ;
}
string Ans = *max_element(v.begin() , v.end()) ;
cout << Ans << "\n" ;
}
int main()
{
__Heart__
int t ; cin >> t ; while(t--) solve() ;
}