//(ᗜ ˰ ᗜ)
// #define NDEBUG
#include <bits/stdc++.h>
using namespace std;
namespace LING
{
#ifdef ONLINE_JUDGE
#define DBG(...) ;
#define dbg(...) ;
#else
#define DBG(x) cout << "! " << #x << " = " << x << endl
// #include "debug.h"
#endif
    using ll = long long;
    using db = double;
#define SPO(x) fixed << setprecision(x)
#define FOR(i, l, r) for (ll i = l; i <= (r); ++i)
#define ROF(i, r, l) for (ll i = r; i >= (l); --i)
#define edl '\n'
#define fir first
#define sec second
#define str string
#define pll pair<ll, ll>
#define heap priority_queue
    // constexpr db PI = acos(-1.0);
    // constexpr db EPS = 1.0e-9;
    constexpr long long LNF = 0x3f3f3f3f3f3f3f3fLL;
    constexpr int INF = 0x3f3f3f3f;
    constexpr long long MOD = 998244353;
    constexpr ll MXN = 1e6 + 5;
    ll KSM(ll base, ll exp, ll MOD)
    {
        ll res = 1;
        base %= MOD;
        while (exp)
        {
            if (exp & 1)
                res = (res * base) % MOD;
            base = (base * base) % MOD;
            exp >>= 1;
        }
        return res;
    }
}
using namespace LING;
ll n, a, b;
ll v[MXN];
void Solve(void)
{
    cin >> n >> a >> b;
    FOR(i, 1, n * 2)
    cin >> v[i];
    sort(v + 1, v + n * 2 + 1);

    FOR(i, 2, n * 2)
    {
        if (v[i] - v[i - 1] > a)
        {
            cout << -1 << edl;
            return;
        }
    }

    ll ans = 0, now = 1;
    while (now < n * 2)
    {
        while (now + 1 <= n * 2 && v[now + 1] - v[now] <= b)
        {
            ++ans;
            now += 2;
        }
        ll tmp = now + 1;
        while (tmp + 2 <= n * 2 && v[tmp + 2] - v[now] <= a && v[tmp + 1] - v[tmp] <= b)
            tmp += 2;
        ans += (tmp - now) / 2;
        now = tmp + 1;
    }
    cout << ans << edl;
    return;
}
int main(void)
{
    ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    // #ifndef ONLINE_JUDGE
    // freopen("cin.txt","r",stdin);
    // freopen("cout.txt","w",stdout);
    // #endif

    int t = 1;
    cin >> t;
    while (t--)
        Solve();
    return 0;
}