#include<bits/stdc++.h>
#define ll long long
#define db double
#define INF 1100000000
#define inf 100000000000000000ll
#define ldb long double
#define pb push_back
#define put_(x) printf("%d ",x)
#define putl_(x) printf("%lld ",x)
#define get(x) x=read()
#define putl(x) printf("%lld\n",x)
#define rep(p,n,i) for(int i=p;i<=n;i+=1)
#define fep(n,p,i) for(int i=n;i>=p;--i)
#define go(x) for(int i=lin[x],tn=ver[i];i;tn=ver[i=nex[i]])
#define pii pair<int,int>
#define mk make_pair
#define gf(x) scanf("%lf",&x)
#define pf(x) ((x)*(x))
#define ui unsigned
#define sq sqrt
#define l(w) t[w].l
#define r(w) t[w].r
#define x(w) t[w].x
#define tag(w) t[w].tag
#define sum(w) t[w].sum
#define sc(A) scanf("%d",&A)
#define scl(A) scanf("%lld",&A)
#define scs(A) scanf("%s",A);
#define put(A) printf("%d\n",A)
#define min(x,y) (x>=y?y:x)
#define max(x,y) (x>=y?x:y)
#define sub(x,y) (x-y<0?x-y+mod:x-y)
#define uint unsigned int
#define mod 1000000007
#define zz p<<1
using namespace std;
const int MAXN=300010,N=2000010;
int n;
ll k;
ll a[MAXN];
int T;
map<ll,int>H;
ll f[MAXN];
ll gcd(ll a,ll b){return b==0?a:gcd(b,a%b);}
void work()
{
	sc(n);scl(k);
	rep(1,n,i)scl(a[i]);
	f[n+1]=0;
	fep(n,1,i)
	{
		f[i]=gcd(f[i+1],a[i]);
	}
	ll c=0;
	H.clear();
	H[0]=0;
	rep(1,n,i)
	{
		c=gcd(c,a[i]);
		H[c]=i;
	}
	ll ans=0;
	for(auto x:H)
	{
		//cout<<x.first<<endl;
		int l=x.second;
		int las=0;
		rep(l+1,n,r)
		{
			ll res=x.first;
			res=gcd(res,las);
			res=gcd(res,f[r+1]);
			res=gcd(res,a[r]+k);
			ans=max(ans,res);
			las=gcd(las,abs(a[r+1]-a[r]));
		}
	}
	putl(ans);
}
int main()
{
	sc(T);
	while(T--)
	{
		work();
	}
	return 0;
}