#include<bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define mp make_pair
#define pb push_back
#define int long long
typedef long long LL;

inline int read(){
	int x = 0 , f = 1 ; char c = getchar() ;
    while( c < '0' || c > '9' ) { if( c == '-' ) f = -1 ; c = getchar() ; } 
    while( c >= '0' && c <= '9' ) { x = x * 10 + c - '0' ; c = getchar() ; } 
    return x * f ;
}

const int maxn = 3e5+20;
int n,k,ans;
int a[maxn],b[maxn][20],gl[maxn],gr[maxn];

int gcd(int x,int y){
	return y ? gcd(y,x % y) : x;
}

int g(int l,int r){
	int d = (r - l + 1);
	int t = log2(d);
	return gcd(b[l][t],b[r - (1<<t) + 1][t]);
}

void solve(){
	n = read();k = read();ans = 0;
	for(int i=1;i<=n;i++) a[i] = read();
	gl[1] = a[1];gr[n] = a[n];
	for(int i=n-1;i>=1;i--) gr[i] = gcd(gr[i+1],a[i]);
	for(int i=2;i<=n;i++) b[i][0] = abs(a[i] - a[i-1]);
	for(int i=1;i<20;i++){
		for(int j=2;j+(1<<i)-1<=n;j++){
			b[j][i] = gcd(b[j][i-1],b[j+(1<<(i-1))][i-1]);
		}
	}
	for(int i=2;i<=n;i++){
		gl[i] = gcd(gl[i-1],a[i]);
		if(gl[i] < gl[i-1]){
			for(int j=i-1;j<=n;j++){
				int tmp = a[j]+k;
				if(i-1!=1) tmp = gcd(tmp,gl[i-2]);
				if(j!=n) tmp = gcd(tmp,gr[j+1]);
				if(i!=j) tmp = gcd(tmp,g(i+1,j));
				ans = max(ans,tmp);
			}
		}
	}
	ans = max(ans,gl[n]);
	if(n==1) ans = max(ans,gl[n] + k);
	else ans = max(ans,gcd(gl[n-1],a[n] + k));
	printf("%lld\n",ans);
}

signed main(){
	// freopen("1.txt","r",stdin);
	int T = 1;
	T = read();
	while(T--) solve();
	return 0;
}