#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 l, r, d, u, a, b;
void solve()
{
    l = d = r = u = 0;
    string s, ans;
    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;
    if (x == a && y == b || a == 0 && b == 0)
    {
        cout << "Impossible" << endl;
        return;
    }

    if (x == a && a == 0)
    {
        if ((y >= b && b > 0) || (y <= b && b < 0))
        {
            cout << "Impossible" << endl;
            return;
        }
    }
    else if (b == y && b == 0)
    {
        if ((x >= a && a > 0) || (x <= a && a < 0))
        {
            cout << "Impossible" << endl;
            return;
        }
    }

    if (b == 0)
    {
        if (u)
            for (; u; u--)
                ans += "U";
        else if (d)
            for (; d; d--)
                ans += "D";
    }
    for (int i = 1; u && i < b; i++, u--)
        ans += "U";
    for (int i = 1; d && -d > b; i++, d--)
        ans += "D";
    if (a == 0)
    {
        if (l)
            for (; l; l--)
                ans += "L";
        else if (r)
            for (; r; r--)
                ans += "R";
    }
    for (int i = 1; l && -i > a; i++, l--)
        ans += "L";
    for (int i = 1; r && i < a; i++, r--)
        ans += "R";
    int mins = min(u, d);
    if (b > 0)
        for (int i = 1; i <= mins; i++)
            ans += "DU";
    else if (b < 0)
        for (int i = 1; i <= mins; i++)
            ans += "UD";
    u -= mins, d -= mins;
    mins = min(l, r);
    if (a > 0)
        for (int i = 1; i <= mins; i++)
            ans += "LR";
    else if (a < 0)
        for (int i = 1; i <= mins; i++)
            ans += "RL";
    l -= mins, r -= mins;
    for (int i = 1; i <= u; i++)
        ans += "U";
    for (int i = 1; i <= d; i++)
        ans += "D";
    for (int i = 1; i <= r; i++)
        ans += "R";
    for (int i = 1; i <= l; i++)
        ans += "L";

    cout << ans << endl;
}

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

    return 0;
}