#include <bits/stdc++.h>
using namespace std;
int main(){
    long long a;
    cin >> a;
    while(a--){
        long long a1,a2,a3,a4;
        cin >> a1 >> a2 >> a3 >> a4;
        if(a1 < a2){
            cout << 0 << endl;
            long long b1 = 64,b2,b3 = 0;
            for(int i = 1;i <= a1 + 114514;i++){
                b2 = rand();
                if(b2 != b1 && b2 >= 65 && b2 <= 80){
                    char t;
                    t = b2;
                    cout << t;
                    b1 = b2;
                    b3++;
                    if(b3 == a1){
                        cout << endl;
                        break;
                    }
                }
            }
        }else{
            if(ceil(a1 / (a2 * 2 - 2)) * a3 > (a2 * 2 - 2) * a4){
            for(int j = 1;j <= floor(a1 / (a2 * 2 - 2));j++){
                long long c1 = 80;
                for(int i = 1;i <= a2 - 2;i++){
                    char c2;
                    c2 = c1;
                    c1--;
                    if(c2 != "aa"){
                        cout << c2;
                    }
                }
                for(int i = 1;i <= 2;i++){
                    cout << "aa";
                }
                c1 = 80;
                for(int i = 1;i <= a2 - 2;i++){
                    char c2;
                    c2 = c1;
                    c1--;
                    if(c2 != "aa"){
                        cout << c2;
                    }
                }
            }
            for(int j = 1;j <= 1;j++){
                long long c1 = 80;
                for(int i = 1;i <= a2 - 2;i++){
                    char c2;
                    c2 = c1;
                    c1--;
                    if(c2 != "aa" && i <= ceil(a1 / (a2 * 2 - 2) - floor(a1 / (a2 * 2 - 2))){
                        cout << c2;
                    }else{
                        break;
                    }
                }
                for(int i = 1;i <= 2;i++){
                    cout << "aa";
                }
                c1 = 80;
                for(int i = 1;i <= a2 - 2;i++){
                    char c2;
                    c2 = c1;
                    c1--;
                    if(c2 != "a" && i <= ceil(a1 / (a2 * 2 - 2) - floor(a1 / (a2 * 2 - 2))){
                        cout << c2;
                    }else{
                        break;
                    }
                }
            }
            }else{
                for(int i = 1;i <= a1;i++){
                    char c2;
                    c2 = c1;
                    c1--;
                    if(c2 != "a"){
                        cout << c2;
                    }else{
                        break;
                    }
                }
            }
        }
    }
    return 0;
}