#include<bits/stdc++.h>
using namespace std;
 
int main(){
	int t,n,k,x,mx;	cin >> t;
	while(t--){
		cin >> n >> k;
		map<int,int> f;
		for(int i=0;i<n;i++){
			cin >> x;
			f[x]++;
		}
		auto it = f.begin();
		//cout << it->first << endl;
		mx = (it->first) + k;
		//cout << "1.mx = " << mx << endl;
		f[mx]++;
		it = f.find(mx);
		if(it->second > 1){
			cout << it->second << endl;
			continue;
		}else{
			cout << "2.mx = " << mx << endl;
			mx--;
			while(f.find(mx) == f.end() && mx > 0) mx--;
			it = f.find(mx);
			f.find(mx) == f.begin() ? cout << "-1\n" : cout << it->second << endl; 
		}
		cout << endl;
 
	}
	return 0;
}

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NAo1IDEKMSAxIDIgMyAxCjQgMgo2IDQgOCA1CjIgMgoxIDYKMyA1CjUgMiA1Cg==

4
5 1
1 1 2 3 1
4 2
6 4 8 5
2 2
1 6
3 5
5 2 5