// I AM A MUSLIM

#include "bits/stdc++.h"

#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")

#define fast_io std::ios::sync_with_stdio(0);std::cin.tie(0)
#define lli long long int
#define flush fflush(stdout)
#define line printf("\n")
#define yn(a, b) printf("%s\n", (a) >= (b) ? "Yes":"No")
#define amodm(a, M) (((a)%M+M)%M)
#define read(s) std::string s;std::cin >> s
#define readL(s) std::string s;getline(std::cin, s)
#define write(s) printf("%s\n", s.c_str())
// #define int lli

using pii = std::pair<int,int>;
const int MOD = 1000000007;
const int mxN = 500100;

signed main() {
    int testCases=1;
    scanf("%d",&testCases);
    
    for (int TC = 1; TC <= testCases; TC++) {
        int n, k, d;
        scanf("%d%d%d",&n,&k,&d);
        int a[n]; for (int i = 0; i < n; i++) scanf("%d",&a[i]);
        int zc = 0, ans = -1, prod = -1, sum = 0;
        for (int i = 0; i < k; i++) {
            sum += a[i];
            if (a[i] == 0) zc++;
        }
        if (sum%d == 0) {
            ans = 1;
            if (zc) prod = 0;
            else prod = 1;
        }
        for (int i = k; i < n; i++) {
            sum -= a[i-k];
            if (a[i-k] == 0) zc--;
            sum += a[i];
            if (a[i] == 0) zc++;
            if (sum%d == 0) {
                int cur_prod = (zc ? 0 : 1);
                if (cur_prod > prod) {
                    ans = i-k+1 + 1;
                    prod = cur_prod;
                }
            }
        }
        printf("%d\n", ans);
    }
    
    return 0;
}