#include<bits/stdc++.h>
using namespace std;
using ll=long long;
const int INF=1e9+10;

ll A,B;

int solve(vector<ll>C){
	int N=C.size()/2;

	vector<int>right(2*N);
	int l=0,r=0;
	while(r<2*N){
		while(r<2*N-1&&C[r+1]-C[r]<=B)r++;
		for(int i=l;i<=r;i++)right[i]=r;

		l=r+1;
		r=l;
	}

	int ret=0;
	int pos=0;
	while(pos<=2*N-2){
		assert(pos%2==0);

		if(C[pos+1]-C[pos]<=B){
			ret++;
			pos+=2;
			continue;
		}

		int nxt_pos=-1;
		int r=pos+1;
		while(C[r]-C[pos]<=A && r<2*N){
			assert(r%2==1);

			int sz=(right[r]-r+1);
			nxt_pos=r;

			if(sz%2==0){
				r=right[r]+1;
			}

			else{
				break;
			}
		}

		assert(nxt_pos%2==1);
		ret+=(nxt_pos-pos-1)/2;

		pos=nxt_pos;
	}

	return ret;
}

int main(){
	int T;cin>>T;
	while(T--){
		int N;cin>>N>>A>>B;
		vector<ll>D(2*N);
		for(int i=0;i<2*N;i++)cin>>D[i];
		sort(D.begin(),D.end());

		vector<ll>C;
		int ans=0;
		bool ok=true;

		for(int i=0;i<2*N;i++){
			ll c=D[i];

			if(C.empty()||c-C.back()<=A){
				C.push_back(c);
			}

			else if(C.size()%2==1){
				ok=false;
			}

			else{
				ans+=solve(C);
				C.clear();
				C.push_back(c);
			}
		}
		if(C.size()%2==0){
			ans+=solve(C);
		}else{
			ok=false;
		}

		if(!ok)ans=-1;
		cout<<ans<<'\n';
	}
}