#include <bits/stdc++.h>
#define int long long
constexpr int N = 1e5 + 5;
constexpr int INF = 1e9 + 5;

int a[N], b[N];
void solve() {
    int n, m;
    std::cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        std::cin >> a[i];
    }
    for (int i = 1; i <= m; i++) {
        std::cin >> b[i];
    }
    std::sort(a + 1, a + n + 1);
    std::sort(b + 1, b + m + 1);
    b[0] = 0, b[m + 1] = INF;

    int ans = 0;
    for (int i = 1; i <= n; i++) {
        int c = a[i];
        int it_b_left = std::lower_bound(b + 1, b + 1 + m, c) - b;
        if (b[it_b_left] == c) continue;
        it_b_left--;
        int it_b_right = std::upper_bound(b + 1, b + 1 + m, c) - b;

        int left = std::max(b[it_b_left], 2 * c - b[it_b_right]);
        int right = std::min(b[it_b_right], 2 * c - b[it_b_left]);
        int it_a_left = std::upper_bound(a + 1, a + 1 + n, left) - a;
        if (it_a_left <= 1) it_a_left = 1;
        int it_a_right = std::lower_bound(a + 1, a + 1 + n, right) - a;
        it_a_right--;
        if (it_a_right >= n) it_a_right = n;
        ans = std::max(ans, it_a_right - it_a_left + 1);
    }

    for (int i = 1; i < n; i++) {
        if ((a[i] + a[i + 1]) % 2 == 0) {
            int c = (a[i] + a[i + 1]) / 2;
            int it_b_left = std::lower_bound(b + 1, b + 1 + m, c) - b;
            if (b[it_b_left] == c) continue;
            it_b_left--;
            int it_b_right = std::upper_bound(b + 1, b + 1 + m, c) - b;

            int left = std::max(b[it_b_left], 2 * c - b[it_b_right]);
            int right = std::min(b[it_b_right], 2 * c - b[it_b_left]);
            int it_a_left = std::upper_bound(a + 1, a + 1 + n, left) - a;
            if (it_a_left <= 1) it_a_left = 1;
            int it_a_right = std::lower_bound(a + 1, a + 1 + n, right) - a;
            it_a_right--;
            if (it_a_right >= n) it_a_right = n;
            ans = std::max(ans, it_a_right - it_a_left + 1);
        } else {
            int c = a[i];
            int it_b_left = std::upper_bound(b + 1, b + 1 + m, c) - b;
            it_b_left--;
            int it_b_right = std::upper_bound(b + 1, b + 1 + m, c) - b;

            int left = std::max(b[it_b_left], a[i] + a[i + 1] - b[it_b_right]);
            int right = std::min(b[it_b_right], a[i] + a[i + 1] - b[it_b_left]);
            int it_a_left = std::upper_bound(a + 1, a + 1 + n, left) - a;
            if (it_a_left <= 1) it_a_left = 1;
            int it_a_right = std::lower_bound(a + 1, a + 1 + n, right) - a;
            it_a_right--;
            if (it_a_right >= n) it_a_right = n;
            ans = std::max(ans, it_a_right - it_a_left + 1);
        }
    }
    if (ans == 0) std::cout << "Impossible\n";
    else std::cout << ans << '\n';
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr), std::cout.tie(nullptr);

    int T;
    std::cin >> T;
    while (T--) {
        solve();
    }
}