#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define all(v)	((v).begin()), ((v).end())
#define sz(v)	((int)((v).size()))
#define Please_Not_Focus_To_My_Code ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
const int mod = 1e9 + 7;
//ceil -> (n + (d - 1))/d
//round+ -> (n + (d/2))/d
//round- -> (n - (d/2))/d
 
void elwkel(){
    ll n , f ,a , b;cin >> n >> f >> a >> b;
    vector<int> arr(n + 1);
    for (int i = 1; i < n + 1; i++) cin >> arr[i];
 
    bool ok = 1;
    for (int i{1}; i < n + 1 && ok; i++){   
        if((arr[i] - arr[i - 1]) * a < b) f -= (arr[i] - arr[i - 1]) * a;
        else f -= b;
        if(f <= 0)ok =0;
    }
 
    cout << (ok ? "YES\n" : "NO\n");
}
 
 
 
int main(){
Please_Not_Focus_To_My_Code;
int t{}; 
cin>> t;
while(t--){
elwkel();
}
}

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6
1 3 1 5
3
7 21 1 3
4 6 10 13 17 20 26
5 10 1 2
1 2 3 4 5
1 1000000000 1000000000 1000000000
1000000000
3 11 9 6
6 8 10
12 621526648 2585904 3566299
51789 61859 71998 73401 247675 298086 606959 663464 735972 806043 806459 919683