#include <bits/stdc++.h>
#define rep(i, a, b) for(int i = (int)a; i <= (int)b; i ++)
#define per(i, a, b) for(int i = (int)a; i >= (int)b; i --)
#define ll long long
using namespace std;
const int maxn = 300010;
int n, lg[maxn];
ll k, a[maxn], pre[maxn], suf[maxn], b[maxn][20];
ll query(int l, int r) {
    int k = lg[r - l + 1];
    return __gcd(b[l][k], b[r - (1 << k) + 1][k]);
}
void solve() {
    cin >> n >> k;
    rep(i, 1, n) cin >> a[i];
    rep(i, 1, n - 1) b[i][0] = abs(a[i] - a[i + 1]);
    rep(j, 1, 18) rep(i, 1, n - (1 << j))
        b[i][j] = __gcd(b[i][j - 1], b[i + (1 << (j - 1))][j - 1]);
    pre[1] = a[1];
    vector < int > positions;
    positions.push_back(0);
    rep(i, 2, n) {
        pre[i] = __gcd(pre[i - 1], a[i]);
        if(pre[i] != pre[i - 1]) positions.push_back(i - 1);
    }
    positions.push_back(n);
    suf[n] = a[n];
    per(i, n - 1, 1) suf[i] = __gcd(suf[i + 1], a[i]);
    ll res = pre[n];
    rep(r, 1, n) {
        for(auto l : positions) {
            if(l + 1 > r) break;
            ll cur = a[r] + k;
            if(l) cur = __gcd(cur, pre[l]);
            if(r < n) cur = __gcd(cur, suf[r + 1]);
            if(l + 1 <= r - 1) cur = __gcd(cur, query(l + 1, r - 1));
            // cout << l << " " << r << " " << cur << endl;
            res = max(res, cur);
        }
    }
    cout << res << '\n';
}
int main() {
#ifdef LOCAL
    freopen("data.in", "r", stdin);
#endif
    ios :: sync_with_stdio(false);
    cin.tie(0);
    lg[1] = 0;
    rep(i, 2, 300000) lg[i] = lg[i >> 1] + 1;
    int T;
    cin >> T;
    while(T --) solve();
    return 0;
}