#include <bits/stdc++.h>

using namespace std;

void test_case(int tc){
    int n, m, k;

    cin >> n >> m >> k;

    vector<char> x, y;
    for (size_t i = 0; i < n; i++){
        char c;
        cin >> c;
        x.push_back(c);
    }
    for (size_t i = 0; i < m; i++){
        char c;
        cin >> c;
        y.push_back(c);
    }

    int k_counter = 0;
    string result = "";
    // We need to keep track of the last one for optimal placement I think
    bool lastChoice = x.front() < y.front();

    sort(x.begin(), x.end());
    reverse(x.begin(), x.end());

    sort(y.begin(), y.end());
    reverse(y.begin(), y.end());

    while(!x.empty() && !y.empty()){
        char cx = x.back(), cy = y.back();

        if(lastChoice != (cx < cy)){
            k_counter = 0;
        }
        
        if(lastChoice == (cx < cy) && k_counter == k){
            k_counter = 0;
            lastChoice = cx >= cy;

            if(cx < cy){
                y.pop_back();
                result.push_back(cy);
            } else {
                x.pop_back();
                result.push_back(cx);
            }
        } else {
            lastChoice = cx < cy;

            if(cx < cy){
                x.pop_back();
                result.push_back(cx);
            } else{
                y.pop_back();
                result.push_back(cy);
            }
        }

        k_counter++;
    }

    cout << result << '\n';
}



int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);

    int t;
    cin >> t;

    for(int tc = 1; tc <= t; ++tc){
        test_case(tc);
    }

    cout << flush;

    return 0;
}