#include <bits/stdc++.h>

using namespace std;

#define F(i, a, b) for (int i = a; i < b; i++)
#define ALL(x) x.begin(), x.end()
#define IOS ios_base::sync_with_stdio(0)

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef long long ll;

vector<ll> a;
ll n, k;

bool valid(int index, ll g, bool opened, bool closed) {
  if (index >= n) {
    return true;
  }

  bool ans = false;
  if (a[index] % g == 0) {
    if (opened) {
      ans |= valid(index + 1, g, true, true);
    } else {
      ans |= valid(index + 1, g, false, false);
    }
  }
  if ((a[index] + k) % g == 0 && !closed) {
    ans |= valid(index + 1, g, true, false);
  }

  return ans;
}

int main() {
  IOS;
  cin.tie(0), cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    cin >> n >> k;
    a = vector<ll>(n);
    F(i, 0, n) { cin >> a[i]; }
    if (n == 1) {
      cout << a[0] + k << '\n';
      continue;
    }
    ll ans = 1;
    ll g = gcd(a[0], a[1]);
    if (valid(2, g, false, false)) {
      ans = max(ans, g);
    }
    g = gcd(a[0] + k, a[1]);
    if (valid(2, g, true, true)) {
      ans = max(ans, g);
    }
    g = gcd(a[0], a[1] + k);
    if (valid(2, g, true, false)) {
      ans = max(ans, g);
    }
    g = gcd(a[0] + k, a[1] + k);
    if (valid(2, g, true, false)) {
      ans = max(ans, g);
    }
    cout << ans << '\n';
  }
}