#include <bits/stdc++.h>
using namespace std;
#define IOS ios::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define endl '\n'
const int N = 2e5 + 5;
#define int long long
typedef pair<int, int> PII;
#define MAX LONG_LONG_MAX
#define mod 10007
#define eps 1e-7
int ar[N];
int l, r, d, u, a, b;
void solve()
{
    l = d = r = u = 0;
    string s;
    cin >> a >> b;

    cin >> s;

    for (char c : s)
    {
        if (c == 'L')
            l++;
        else if (c == 'R')
            r++;
        else if (c == 'U')
            u++;
        else
            d++;
    }
    int x = r - l, y = u - d;

    PII pot = {x, y};
    if (pot.first == a && pot.second == b || a == 0 && b == 0)
    {
        cout << "Impossible" << endl;
        return;
    }


    if (x == a && a == 0)
    {
        if ((u - d > b && b > 0) || (u - d < b && b < 0))
        {
            cout << "Impossible" << endl;
            return;
        }
    }
    if (b == y && b == 0)
    {
        if ((r - l > a && a > 0) || (r - l < a && a < 0))
        {
            cout << "Impossible" << endl;
            return;
        }
    }

    if (a == x)
    {

        if (b > 0)
        {
            for (int i = 1; i <= d; i++)
                cout << "D";
            for (int i = 1; i <= u; i++)
                cout << "U";
        }
        else
        {
            for (int i = 1; i <= u; i++)
                cout << "U";
            for (int i = 1; i <= d; i++)
                cout << "D";
        }
        if (a > 0)
        {
            for (int i = 1; i <= r; i++)
                cout << "L";
            for (int i = 1; i <= l; i++)
                cout << "R";
        }
        else
        {
            for (int i = 1; i <= l; i++)
                cout << "R";
            for (int i = 1; i <= r; i++)
                cout << "L";
        }
    }
    else
    {

        if (a > 0)
        {
            for (int i = 1; i <= r; i++)
                cout << "L";
            for (int i = 1; i <= l; i++)
                cout << "R";
        }
        else
        {
            for (int i = 1; i <= l; i++)
                cout << "R";
            for (int i = 1; i <= r; i++)
                cout << "L";
        }
        if (b > 0)
        {
            for (int i = 1; i <= d; i++)
                cout << "D";
            for (int i = 1; i <= u; i++)
                cout << "U";
        }
        else
        {
            for (int i = 1; i <= u; i++)
                cout << "U";
            for (int i = 1; i <= d; i++)
                cout << "D";
        }
    }
    cout << endl;
}

signed main()
{
    int t;
    cin >> t;
    while (t--)
        solve();

    return 0;
}