#include<bits/stdc++.h>
#define ll long long

using namespace std;

const int N = 1e5 + 10;
int n, x, y;
string t = "LRDU", res, s;
map<char, int>ha;

int cnt[4];

void out(int i)
{
    while (cnt[i]--)cout << res[i];
}

void solve()
{
    cin >> x >> y >> s;
    res = t;
    for (int i = 0; i < 4; i++)cnt[i] = 0;
    for (auto k : s)cnt[ha[k]]++;
    if (x < 0)x = -x, swap(cnt[0], cnt[1]), swap(res[0], res[1]);
    if (y < 0)y = -y, swap(cnt[2], cnt[3]), swap(res[2], res[3]);
    if (-cnt[0] + cnt[1] == x && -cnt[2] + cnt[3] == y)cout << "Impossible\n";
    else {
        if (cnt[1] - cnt[0] == x) {
            swap(cnt[0], cnt[2]), swap(cnt[1], cnt[3]), swap(x, y), swap(res[0], res[2]), swap(res[1], res[3]);
        }
        if (y == 0 && cnt[1] >= cnt[0] + x && cnt[2] == 0 && cnt[3] == 0)cout << "Impossible\n";
        else if (y == 0) {
            if (cnt[2])cnt[2]--, cout << res[2];
            else if (cnt[3])cnt[3]--, cout << res[3];
            for (int i = 0; i < 4; i++)out(i);
            cout << '\n';
        }
        else {
            for (int i = 0; i < 4; i++)out(i);
            cout << "\n";
        }
    }
}

int main()
{
    ha['L'] = 0, ha['R'] = 1, ha['D'] = 2, ha['U'] = 3;
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1; cin >> t;
    while (t--)solve();
    return 0;
}