#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fast ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
void solve();
using pii = pair<int, int>; 
using db = double;
signed main(){
	fast
	int t = 1;
	cin >> t;
	for(int i = 1; i <= t; i++){
		solve();
	}
}

const int N = 1e6 + 10, M = N * 2, P = 998244353;

int n, a, b;
int w[N];

void solve(){
	cin >> n >> b >> a;
	for(int i = 1; i <= 2 * n; i++){
		cin >> w[i];
	}
	sort(w + 1, w + 2 * n + 1);
	int res = 0;
	for(int i = 1; i <= 2 * n; i += 2){
		if(w[i + 1] - w[i] > b){
			cout << -1 << '\n';
			return;
		}
		if(w[i + 1] - w[i] <= a){
			res++;
			continue;
		}
		int j = i + 1;
		while(j + 2 <= 2 * n && (w[j + 1] - w[j] <= a && w[j + 2] - w[i] <= b)){
			res++;
			j += 2;
		}
		i = j + 1;
	}
	cout << res << '\n';
}