#include <bits/stdc++.h>
#define IOS ios::sync_with_stdio(false);cin.tie(0); 
#define int long long
using namespace std;

signed main() {
    IOS;
    int t;
    cin >> t;
    while (t--) {
        int mx, my;
        cin >> mx >> my;
        string str;
        cin >> str;
        vector<int> cnt(4, 0);  // U, D, L, R
        for (char ch : str) {
            if (ch == 'U') cnt[0]++;
            else if (ch == 'D') cnt[1]++;
            else if (ch == 'L') cnt[2]++;
            else if (ch == 'R') cnt[3]++;
        }

        int up = cnt[0], down = cnt[1], left = cnt[2], right = cnt[3];

        // Calculate the potential range for x and y the robot can reach
        int min_x = -left, max_x = right;
        int min_y = -down, max_y = up;

        // Check if the mine is within the reachable range
        if (mx >= min_x && mx <= max_x && my >= min_y && my <= max_y) {
            // Calculate remaining moves needed to avoid the mine
            int rem_x = mx - min_x;  // Remaining x moves to reach the mine
            int rem_y = my - min_y;  // Remaining y moves to reach the mine

            if ((mx == 0 && my == 0) || 
                (rem_x >= 0 && rem_x <= right - left && rem_y >= 0 && rem_y <= up - down)) {
                cout << "Impossible" << endl;
            } else {
                // Construct a valid path avoiding the mine
                string result;
                result += string(up, 'U');
                result += string(down, 'D');
                result += string(left, 'L');
                result += string(right, 'R');
                cout << result << endl;
            }
        } else {
            // Construct a valid path avoiding the mine
            string result;
            result += string(up, 'U');
            result += string(down, 'D');
            result += string(left, 'L');
            result += string(right, 'R');
            cout << result << endl;
        }
    }
    return 0;
}