/* 
 *   @author:- MAHMUDUL HASAN SAKIB
 *   DATE & TIME :- 2025-04-06 20:28:48
 *   BANGLADESH , SYLHET.
 */ 
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <deque>
#include <forward_list>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <optional>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
#define fi first
#define se second
#define endl '\n'
#define ll long long
#define ull unsigned long long
#define ld long double
#define PI acos(-1.0)
#define pb push_back
#define mp make_pair
#define vi vector<ll>
#define maxn 500005
#define mod 1000000007
#define inf 1000000007
#define pii pair<ll,ll>
#define vii vector<pii>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define lcm(a,b) ((a*b)/__gcd(a,b));
#define srt(v) sort(v.begin(),v.end())
#define rsrt(v) sort(v.rbegin(),v.rend())
#define setbits(x) __builtin_popcountll(x)
#define rep(i, a, b) for(ll i = (a); i < (b); i++)
#define per(i, a, b) for(int i = (a); i >= (b); i--)
#define rev_str(str) reverse(str.begin(),str.end());
#define print(v) for(auto e:v) cout<<e<<" "; cout<<endl;
#define sum(a) (accumulate((a).begin(), (a).end(), 0LL))
#define printp(v) for(auto e:v) cout<<e.first<<" "<<e.second<<endl;
#define fast ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
bool sortByValue(const pair<int, int>& a, const pair<int, int>& b) {return a.second > b.second;}
const int M = 1e9+7;
bool is_Prime(ll n) {
    if (n < 2) return false; 
    for (ll i = 2; i * i <= n; ++i) {
        if (n % i == 0) return false; 
    }
    return true; 
}
long long Pow(ll a,ll b){
    ll ans = 1;
    while(b>0){
        if(b&1) ans*=a;
        b>>=1;
        a*=a;
    }
    return ans;
}
long long modPow(ll a,ll b){
    ll ans = 1;
    while(b>0){
        if(b&1) ans=(ans*a)%mod;
        b>>=1;
        a=(a*a)%mod;
    }
    return ans;
}
// lies between divisor of a and b == GCD
// prime factorization while the taking the maximum power ==LCM...
ll gcd(ll a, ll b) {
    while (b != 0) {
        ll temp = b;
        b = a % b;
        a = temp;
    }
    return a;
}
 
ll Lcm(ll a, ll b) {
    return (a / gcd(a, b)) * b;
}

void solve(){
    ll n,k,d;cin>>n>>k>>d;
    vi p(n),pre(n+1,0);

    rep(i,0,n) {
        cin>>p[i];
        pre[i+1] = pre[i]+p[i];
    }
    // ll sum = 0;
    // rep(i,0,k){
    //     sum+= p[i];
    // }
    // ll mx_pro=0,start=0;
    // if(sum%d==0){
    //     ll pro = 1;
    //     rep(i,0,k){
    //         pro*=p[i];
    //     }
    //     if(pro>mx_pro){
    //         mx_pro = pro;
    //         start = 1;
    //     }
    // }
    ll best = -1;
    ll ans = -1;
    bool ok = false;
    rep(i,0,n){
        if(i+k<=n){
            ll ji  = pre[i+k]-pre[i];
            if(ji%d==0){
                ll one = p[i];
                rep(j,i+1,k){
                    one *= p[j];
                }
                if(one>best) {
                    ok = true;
                    best = one;
                    ans = i+1;
                    //cout<<i+1<<endl;return;
                }
            }
        }
    }
    cout<<ans<<endl;
    
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll t=1;cin>>t;
    while(t--){
        solve();
    }
    return 0;
}