// Author: Shawn Das Shachin-->(shawn_das)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define pb push_back
#define mod 1000000007
#define srt(v) sort(v.begin(),v.end())
#define rsrt(v) sort(v.rbegin(),v.rend())
#define OPTIMIZE_IO ios::sync_with_stdio(false); cin.tie(nullptr);
#define setbit(x) __builtin_popcount(x);
#define printp(v) { for(auto &it : v) std::cout << it.first << " " << it.second << std::endl; }
#define printarr(arr) { for(auto &it : arr) std::cout << it << " "; std::cout << std::endl; }

void solve() {
    int n,k,d;
    cin>>n>>k>>d;
    
    vector<int> v(n);
    for(int i=0; i<n; i++)cin>>v[i];
   
    ll sum = 0;
    ll prod = 1;
    for(int i = 0; i < k; i++) {
        sum += v[i];
        prod *= v[i];
    }
    if(sum % d == 0) {
        cout<<1<<endl;
        return;
    }
    
    for(int i=1; i<= n-k; i++) {
        sum -=v[i-1];
        sum +=v[i+k- 1];
        if(sum !=k){
                prod=0;
        }else{
                prod=1;
        }
        
        if(sum%d == 0) {
            cout<<i+1<<endl;
            return;
        }
    }
    
    cout << -1 << endl;
}


int main() {
    OPTIMIZE_IO;
    int t;
    cin>>t;
    while(t--){
        solve();
    }
}