#include<bits/stdc++.h>
using namespace std;
#define ll long long int 
//const int sz = 1e3 + 3, mod = 998244353;
string sum(string a, string b) {
    string ans = "";
    int n = a.size();
    int m = b.size();
    int cary = 0;
    int i = n - 1;
    int j = m - 1;
    while(i >= 0 || j >= 0 || cary) {
        if(i >= 0) {
            cary += (a[i] - '0'); 
            i--;
        }
        if(j >= 0) {
            cary += (b[j] - '0'); 
            j--;
        }
        ans += char('0' + (cary % 10));
        cary /= 10;
    }
    reverse(ans.begin(), ans.end());
    //cout << a << " " << b << " " << ans << "\n";
    return ans;
}
bool cmp(string a, string b) {
    if(a.size() != b.size()) return a.size() < b.size();
    return a < b;
}
int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int t; cin >> t;
    while(t--) {
        int n, k; cin >> n >> k;
        string c; cin >> c;
        string ans = c;
        int limit = 1;
        for(int i = 1; i <= k; i++, limit *= 3);
        for(int i = 0; i < limit; i++) {
            int i1 = i;
            std::vector<int> v;
            int sum1 = 0;
            int tot = 0;
            for(int j = 0; j < k; j++) {
                int len = - 1 + (i1 % 3);
                v.push_back(len);
                tot += sum1 + len;
                sum1 += len;
                i1 /= 3;
            }
            if(tot >= n || (n - tot) % (k + 1)) continue;
            int prt = (n - tot) / (k + 1);
            int lst = prt;
            
            string crt = c.substr(0, prt);
            //cout << i << "\n";
            //for(int &u:v) cout << u << " "; cout << "\n";
            //cout << prt << "\n";
            int pos = 1;
            for(int j = 0; j < k; j++) {
                if(prt + v[j] < 1) {
                    pos = 0;
                    break;
                }
                crt = sum(crt, c.substr(lst, prt + v[j]));
                lst += prt + v[j];
                prt += v[j];
            }
            //cout << crt << "\n";
            if(pos)
            if(cmp(crt, ans)) ans = crt;
        }
        cout << ans << "\n";
    }
    return 0; 
}