#include<bits/stdc++.h>
using namespace std;

#define print(a) for(auto x:a)cout<<x<<' ';cout<<'\n';
#define debug(x) cout<<#x<<" "<<x<<'\n'
#define int   long long int

const int M = 1e9 + 7;
const int N = 2e5 + 10;

void solve(){
   int n, k;
   cin >> n >> k;

   vector<string> a(n);
   for(int i = 0; i < n; i++){
      int x; cin >> x;
      a[i] = to_string(x);
   }

   string res;
   
   for(int i = max(0ll, n - k - 1); i >= 0; i--){
      string s = "";
      for(int j = i, cnt = k + 1; j < n && cnt--; j++){
         s += a[j];
      }
      if(res.size() < s.size()) res = s;
      else if(s.size() == res.size()) res = max(res, s);
   }
   cout << res << '\n';

}

signed main() {
   ios_base::sync_with_stdio (0);
   cin.tie (0);

   int t = 1;   cin >> t;
   for (int tc = 1; tc <= t; tc++) {
      //cout<<"Case "<<tc<<": ";
      solve();
   }
   return 0;
}