#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int MOD = 1000000007;
#define sz(x) (ll)(x).size()
#define rd ({ll x; cin >> x; x; })
#define dbg(x) cerr << "[" #x "]  " << (x) << "\n"
// #define errv(x) {cerr << "["#x"]  ["; for (const auto& ___ : (x)) cerr << ___ << ", "; cerr << "]\n";}
// #define errvn(x, n) {cerr << "["#x"]  ["; for (auto ___ = 0; ___ < (n); ++___) cerr << (x)[___] << ", "; cerr << "]\n";}
// #define cerr if(0)cerr
#define xx first
#define yy second
mt19937 rnd(std::chrono::high_resolution_clock::now().time_since_epoch().count());
/*_________________________________________________________________________________________________________________________*/

void Solve()
{
    ll n, k, d;
    cin >> n >> k >> d;
    vector<ll> arr(n);
    for (ll i = 0; i < n; i++) {
        cin >> arr[i];
    }
    ll sum = 0;
    for (int i = 0; i < k - 1; i++) {
        sum += arr[i];
    }
    ll ans = -2;
    for (int i = k - 1; i < n; i++) {
        sum += arr[i];
        if (sum % d == 0) {
            if (ans == -2) {
                ans = i - k + 1;
            }
            if (sum == k) {
                ans = i - k + 1;
                break;
            }
        }
        sum -= arr[i - k + 1];
    }
    cout << ++ans << '\n';
}

int32_t main()
{
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1;
    cin >> t;
    for (int i = 1; i <= t; i++) {
        // cout << "Case #" << i << ": "; // cout << "Case " << i << ": ";
        Solve();
    }
    return 0;
}
// Coded by Tahsin Arafat (@TahsinArafat)