#include <bits/stdc++.h>
using namespace std;
using ll = long long;

void solve()
{
    ll n, k;
    cin >> n >> k;
    vector<ll> a(n);
    for (int i = 0; i < n; ++i) cin >> a[i];
    set<ll> s;
    ll g = 0;
    for (int i = 0; i < n; ++i)
    {
        g = __gcd(g, a[i]);
        s.insert(g);
    }
    g = 0;
    for (int i = n - 1; i >= 0; --i)
    {
        g = __gcd(g, a[i]);
        s.insert(g);
    }
    ll ans = 1;
    for (auto e : s)
    {
        vector<int> v;
        vector<ll> t(a);
        bool f = 1;
        for (int i = 0; i < n; ++i)
        {
            if (a[i] % e && (a[i] + k) % e == 0) v.push_back(i);
        }
        if (v.size())
        {
            int lef = *min_element(v.begin(), v.end());
            int rig = *max_element(v.begin(), v.end());
            for (int i = lef; i <= rig; ++i) t[i] += k;
        }
        for (int i = 0; i < n; ++i)
        {
            if (t[i] % e) f = 0;
        }
        if (f) ans = e;
    }
    g = 0;
    for (int i = 0; i < n; ++i) g = __gcd(g, a[i] + k);
    cout << max(g, ans) << '\n';
    return;
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int T = 1;
    cin >> T;
    while (T--) solve();
    return 0;
}