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

void solveCase()
{
    int n, critical, acceptable;
    cin >> n >> critical >> acceptable;
    n <<= 1;
    vector<lli> v(n);
    for (int i = 0; i < n; i++)
    {
        cin >> v[i];
    }
    sort(v.begin(), v.end());
    int solution = 0;
    for (int i = 0; i < n; i+=2)
    {
        int diff = v[i+1]-v[i];
        if (diff <= acceptable)
        {
            solution++;
        }
        else if (diff > critical)
        {
            cout << "-1\n"; return;
        }
        else
        {
            int beginning = v[i];
            while (i + 3 < n && v[i+3]-beginning <= critical && v[i+2] - v[i+1] <= acceptable)
            {
                i+=2; solution++;
            }
        }
    }
    cout << solution << "\n";
}

int main()
{
    int n; cin >> n; while (n--)
    {
        solveCase();
    }
    return 0;
}