#include<bits/stdc++.h>
#define endl '\n'
using namespace std;
using ll = long long;

void solve() {
    int n, k, d;
    cin >> n >> k >> d;
    vector<bool> v(n);

    for(int i = 0; i < n; i++) {
        int x; cin >> x;
        v[i] = x;
    }
    int sum = 0;
    for(int i = 0; i < k - 1; i++) {
        sum += v[i];
    }
    int ans = -1;
    for(int i = k - 1; i < n; i++) {
        sum += v[i];
        if(sum % d == 0) {
            if(sum == k) {
                cout << i - k + 2 << endl;
                return;
            }
            else if(ans == -1) ans = i - k + 2;
        }
        sum -= v[i - k + 1];
    }
    cout << ans << endl;
    return;
}

int main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int tc = 1;
    cin >> tc;
    for (int t = 1; t <= tc; t++) {
        // cout << "Case " << t << ": ";
        solve();
    }
    return 0;
}