2015 HIAST Collegiate Programming Contest 

#include <iostream>
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll a[100005];
ll c[100005];
const int mod = 1000000007;
ll qpow(ll a, ll k)  // 快速幂取模
{
    ll res = 1;
    while(k)
    {
        if(k % 2) res *= a;
        res %= mod;
        k /= 2;
        a = (a * a) % mod;
    }
    return res % mod;
}
ll C(ll n, ll m)
{
    if(m > n) return 0;
    c[0] = 1;
    for(ll i = 1; i <= m; i ++)
    {
        c[i] = ((c[i - 1] * (n - i + 1))%mod) * qpow(i, mod - 2); // 逆元
        c[i] %= mod;
    }
    return c[m] % mod;
}
int main()
{
    ll n,m,i,j,k,d;
    ll t;
    ll numd = 0;
    scanf("%lld",&t);
    while(t--)
    {
        scanf("%lld %lld %lld %lld", &n, &m, &k, &d);
        numd = 0;
        for(i = 1; i <= n; i ++)
        {
            scanf("%lld", &a[i]);
            if(a[i] >= d) numd ++;
        }
        ll ans = 0;
        ll nn = min(numd,m);
        for(i = k; i <= nn; i ++)
        {
            ans += C(numd,i) * C(n - numd, m - i);
        }
        ans %= mod;
        printf("%lld\n",ans);
    }
    return 0;
}