#include<bits/stdc++.h>
#define ll long long
#define F(x,y,z) for(int x=(y);x<=(z);x++)
using namespace std;
const int N=300010;
int n;
ll k;
ll a[N];
ll pre[N],suf[N];
ll ans;
ll gcd(ll a,ll b){
    if(!b) return a;
    return gcd(b,a%b);
}
void solve(){
    cin>>n>>k;
    ans=0;
    ll g;
    for(int i=1;i<=n;i++) cin>>a[i];
    pre[1]=a[1];g=a[1]+k;
    for(int i=2;i<=n;i++){
        pre[i]=gcd(pre[i-1],a[i]);
        g=gcd(g,a[i]+k);
        // cout<<i<<' '<<pre[i]<<endl;
    }
    suf[n]=a[n];
    for(int i=n-1;i>=1;i--) suf[i]=gcd(suf[i+1],a[i]);
    ans=max(ans,pre[n]);ans=max(ans,g);
    for(int i=2;i<=n;i++)
        if(pre[i]!=pre[i-1]){
            // cout<<i<<endl;
            ll sum=pre[i-1];
            // cout<<sum<<endl;
            for(int j=i;j<=n;j++){
                sum=gcd(sum,a[j]+k);
                // cout<<sum<<' ';
                if(j<n) ans=max(ans,gcd(sum,suf[j+1]));
            }
            // cout<<endl;
            ans=max(ans,sum);
        }
    cout<<ans<<endl;
}
int main(){
    int T;
    cin>>T;
    while(T--) 
        solve();
    return 0;
}