#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N = 2e3 + 5;
int a[N];
int b[N];int n, m;
int c[N];
int coun[N];
double l[N], r[N];
void solve()
{
	
	int x, y;
	cin >> x >> y;
	if (x == 0 && y == 0)
	{
		cout << "Impossible" << endl;
		return;
	}
	string s;
	cin >> s;
	memset(a, 0, sizeof(a));
	for (int i = 0; i < s.size(); i++)
	{
		if (s[i] == 'U') a[0]++;
		if (s[i] == 'D') a[1]++;
		if (s[i] == 'L') a[2]++;
		if (s[i] == 'R') a[3]++;

	}
	if (((a[0] - a[1]) == y) && ((a[3] - a[2]) == x))
	{
		cout << "Impossible" << endl;
		return;
	}
	else if ((a[2] == 0 && a[3] == 0))
	{
		if (y >0 && a[0] - a[1] > y)
		{
			cout << "Impossible" << endl;
			return;
			
		}
		if (y < 0 && a[0] - a[1] < y)
		{
			cout << "Impossible" << endl;
			return;
			
		}
	}
	else if ((a[0] == 0 && a[1] == 0))
	{
		if (x >0 && a[3] - a[2] > x)
		{
			cout << "Impossible" << endl;
			return;
			
		}
		if (x < 0 && a[3] - a[2] < x)
		{
			cout << "Impossible" << endl;
			return;
			
		}
	}
	
	if (a[0]-a[1]==y )
	{
		if (y == 0)
		{
			cout << "U";
		for (int i = 0; i < a[3]; i++) cout << "R";
		for (int i = 0; i < a[2]; i++) cout << "L";
		for (int i = 0; i < a[0]-1; i++) cout << "U";
		for (int i = 0; i < a[1]; i++) cout << "D";
		

		}
		else
	{
		for (int i = 0; i < a[3]; i++) cout << "R";
		for (int i = 0; i < a[2]; i++) cout << "L";
		for (int i = 0; i < a[1]; i++) cout << "D";
		for (int i = 0; i < a[0]; i++) cout << "U";
	}
	

	}

	else if (a[3] - a[2] == x)
	{
			for (int i = 0; i < a[1]; i++) cout << "D";
			for (int i = 0; i < a[0]; i++) cout << "U";
			for (int i = 0; i < a[3]; i++) cout << "R";
			for (int i = 0; i < a[2]; i++) cout << "L";
			
		


	}
	else
	{
		for (int i = 0; i < a[3]; i++) cout << "R";
		for (int i = 0; i < a[2]; i++) cout << "L";
		for (int i = 0; i < a[1]; i++) cout << "D";
		for (int i = 0; i < a[0]; i++) cout << "U";
	}
	cout << endl;

}
signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int t;
	cin >> t;
	while (t--)
	{
		solve();
	}
	
}