#include <iostream> 
#include<vector>
#include<string>
#include<algorithm>
#include <cstring>
#include<ctype.h>
#include<set>
#include<map>
#include<cmath>
#include<climits>
#include<stack>
#include<list>
#include<queue>
#include<unordered_map>
#include<unordered_set>
#define IOS ios::sync_with_stdio(false);cin.tie(0); 
#define maxn 100+5
#define ll long long
using namespace std;
const int mod = 1e8;


signed main() {
	int t;
	cin >> t;
	string s = "UDLR";
	while (t--)
	{
		int x, y;
		vector<int>cnt(5, 0);
		cin >> x >> y;
		string str;
		cin >> str;

		for (int i = 0; i < str.size(); i++)
		{
			if (str[i] == s[0])
				cnt[0]++;
			if (str[i] == s[1])
				cnt[1]++;
			if (str[i] == s[2])
				cnt[2]++;
			if (str[i] == s[3])
				cnt[3]++;
		}
		int up = cnt[0]; int down = cnt[1]; int left = cnt[2]; int right = cnt[3];
		down = -down; left = -left;
		bool flag1 = true;
		bool flag2 = true;
		int len = str.size();
		int a = 0;
		int b = 0;
		string path;
		if (x == 0 && y == 0)
		{
			cout << "Impossible"<<endl;
			continue;
		}
		if (up + down == y&&left+right==x)
		{
			cout << "Impossible"<<endl;
			continue;
		}
		if (up >= y && down == 0 && left == 0 && right == 0 ||
			(down <= y && up == 0 && left == 0 && right == 0) ||
			(left <= x && down == 0 && up == 0 && right == 0) ||
			(right >=x && up == 0 && down == 0 && left == 0))
		{
			cout << "Impossible" << endl;
			continue;
		}
		/*cout << up << " " << down << endl;*/
		if (up + down != y)
		{
			while (up)
			{
				up--;
				path.push_back(s[0]);
			}
			while (down<0)
			{
				down++;
				path.push_back(s[1]);
			}
			while (left<0)
			{
				left++;
				path.push_back(s[2]);
			}
			while (right)
			{
				right--;
				path.push_back(s[3]);
			}
			cout << path << endl;
			continue;
		}
		
		if (left + right != x)
		{
			while (left <0)
			{
				left++;
				path.push_back(s[2]);
			}
			while (right)
			{
				right--;
				path.push_back(s[3]);
			}
			while (up)
			{
				up--;
				path.push_back(s[0]);
			}
			while (down < 0)
			{
				down++;
				path.push_back(s[1]);
			}
			
			cout << path << endl;
			continue;
		}
		

	}


}