#include <bits/stdc++.h>
using namespace std;
#define int long long

template<class Fun> class y_combinator_result {
  Fun fun_;
public:
  template<class T> explicit y_combinator_result(T &&fun): fun_(std::forward<T>(fun)) {}
  template<class ...Args> decltype(auto) operator()(Args &&...args) { return fun_(std::ref(*this), std::forward<Args>(args)...); }
};
template<class Fun> decltype(auto) y_combinator(Fun &&fun) { return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun)); }

template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
template<typename... Args> ostream& operator<<(ostream& os, const tuple<Args...>& t) { os << '('; apply([&os](const Args&... args) { size_t n = 0; ((os << args << (++n != sizeof...(Args) ? ", " : "")), ...); }, t); return os << ')'; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }

template<typename T>ostream& operator<<(ostream& os, queue<T>& _q) { queue<T> q = _q; os << '{'; string sep; while (!q.empty()) { os << sep << q.front(); sep = ", "; q.pop(); } return os << '}';}
template<typename T>ostream& operator<<(ostream& os, stack<T> st) { os << '{'; string sep; while (!st.empty()) { os << sep << st.top(); sep = ", "; st.pop(); } return os << '}';}
template<typename T, typename Container, typename Compare>ostream& operator<<(ostream& os, priority_queue<T, Container, Compare> pq) { os << '{'; string sep; while (!pq.empty()) { os << sep << pq.top(); sep = ", "; pq.pop(); } return os << '}';}
template<size_t N>ostream& operator<<(ostream& os, const bitset<N>& bs) { return os << bs.to_string();}

void debug_out() { cout << endl; }
template<typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cout << ' ' << H; debug_out(T...); }
#ifdef LOCAL_DEBUG
  #define debug(...) cout << "[Line " <<  __LINE__ << "] (" << #__VA_ARGS__ << "):", debug_out(__VA_ARGS__)
#else
  #define debug(...)
#endif

/*
  
*/

void run_case() {
  int n, k, d;
  cin >> n >> k >> d;
  vector<int> a(n);
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  
  int sum = 0, zeros = 0;
  int maxProd = -1, maxIdx = -2;
  for (int i = 0; i < n; i++) {
    sum += a[i];
    zeros += !a[i];

    if (i >= k) {
      sum -= a[i - k];
      zeros -= !a[i - k];
    }

    if (i >= k - 1 && sum % d == 0) {
      int prod = (zeros ? 0 : 1);
      if (prod > maxProd) {
        maxProd = prod;
        maxIdx = i - k + 1;
      }
    }
  }
  cout << ++maxIdx << '\n';
}

signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cin.exceptions(cin.failbit);

  int T = 1;
  cin >> T;
  for (int t = 1; t <= T; t++) {
    // cout << "Case #" << t << ": ";
    run_case();
  }

  return 0;
}