#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define ll long long int
#define vv vector<long long>
#define mpp map<long long,long long>
#define ss set<long long>
#define vp vector<pair<long long, long long>>
#define MOD 1000000007
#define YES cout<<"YES"<<endl
#define NO cout<<"NO"<<endl
#define all_v v.begin(),v.end()
#define all_a a.begin(),a.end()
#define sort_rev sort(v.rbegin(),v.rend());
#define all_n for(int i=0;i<n;i++)
#define print for(auto it:v)cout<<it<<" "
#define print_vp for(auto it:vp)cout<<it.first<<" "<<it.second<<endl
#define print_mp for(auto it:mp) cout<<it.first<<" "<<it.second<<endl
void requisite(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);cout.tie(nullptr);
}
int main() {
    requisite();
    ll t;
    cin>>t;
    while (t--){
        ll n,k;
        cin>>n>>k;
        vv v(n);
        all_n{
            cin>>v[i];
        }
        vector<string>s(n-k+1);
        for (int i = 0; i <= n-k; ++i) {
            for (int j = i; j <= i+k; ++j) {
                s[i]=s[i].append((to_string(v[j])));
            }
        }
        string a="";
        for (int i = 0; i <n-k; ++i) {
//            cout<<s[i]<<endl;
            if (s[i].size()>a.size()){
                a=s[i];
            }
            else if (s[i].size()==a.size()){
                int l=0;
                while (l<s[i].size()) {
                    ll x = s[i][l] - '0';
                    ll y = a[l] - '0';
                    if (x > y) {
                        a = s[i];
                        break;
                    }
                    else if (y>x){
                        break;
                    }
                    else l++;
                }
            }
        }
        cout<<a<<endl;
    }
    return 0;
}