#include <iostream>
#include <vector>
using namespace std;

int main() {
    int t;
    cin >> t;

    while (t--) {
        int N, K, D;
        cin >> N >> K >> D;

        vector<int> A(N);
        for (int i = 0; i < N; ++i)
            cin >> A[i];

        int bestIndex = -1;
        int maxProduct = -1;

        int windowSum = 0;
        int zeroCount = 0;

        for (int i = 0; i < K; ++i) {
            windowSum += A[i];
            if (A[i] == 0) zeroCount++;
        }

       
        if (windowSum % D == 0) {
            int currentProduct = (zeroCount == 0) ? 1 : 0;
            if (currentProduct > maxProduct) {
                maxProduct = currentProduct;
                bestIndex = 0;
            }
        }

       
        for (int i = K; i < N; ++i) {
            // Remove A[i - K], add A[i]
            if (A[i - K] == 0) zeroCount--;
            windowSum -= A[i - K];

            if (A[i] == 0) zeroCount++;
            windowSum += A[i];

            if (windowSum % D == 0) {
                int currentProduct = (zeroCount == 0) ? 1 : 0;
                if (currentProduct > maxProduct) {
                    maxProduct = currentProduct;
                    bestIndex = i - K + 1;
                }
                
                else if (currentProduct == maxProduct && bestIndex > i - K + 1) {
                    bestIndex = i - K + 1;
                }
            }
        }

        if (bestIndex == -1)
            cout << -1 << endl;
        else
            cout << (bestIndex + 1) << endl; // Convert to 1-based index
    }

    return 0;
}