#include <bits/stdc++.h>

using namespace std;

#define F(i, a, b) for (int i = a; i < b; i++)
#define ALL(x) x.begin(), x.end()
#define IOS ios_base::sync_with_stdio(0)

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef long long ll;

int main() {
  IOS;
  cin.tie(0), cout.tie(0);
  int t, n;
  ll a, b;
  cin >> t;
  while (t--) {
    cin >> n >> a >> b;
    vector<ll> students(2 * n);
    F(i, 0, 2 * n) { cin >> students[i]; }
    sort(ALL(students));
    bool possible = true;
    F(i, 0, n) {
      if (students[2 * i + 1] - students[2 * i] > a) {
        possible = false;
        break;
      }
    }
    if (!possible) {
      cout << -1 << '\n';
      continue;
    }

    int ans = 0;
    int index = -1;
    F(i, 0, 2 * n) {
      if (i == index) {
        index = -1;
        continue;
      }
      if (students[i + 1] - students[i] <= b) {
        i++;
        ans++;
      } else {
        if (index == -1) {
          index = upper_bound(ALL(students), students[i] + a) -
                  students.begin() - 1;
        } else {
          index = -1;
        }
      }
    }
    cout << ans << '\n';
  }
}