#include<bits/stdc++.h>
using namespace std;
#define ll long long
// R = x+1 = 1   L = x-1 = 2   U = y + 1 = 3  D = y - 1 = 4
int cnt[5];
void slove()
{
	int flag = 0 ;
	ll x,y;
	x = 0;
	y = 0;
	ll mx,my;
	string s;
	cin>>mx>>my;
	cin>>s;
	for(int i = 0 ; i < s.size() ; i++)
	{
		if(s[i]=='R')
		{
			cnt[1]++;
			x++;
//			cout<<x<<endl;
			if(x==mx&&y==my)
			flag = 1 ;
			continue;
		}
		if(s[i]=='L')
		{
			cnt[2]++;
			x= x - 1;
			if(x==mx&&y==my)
			flag = 1 ;
			continue;
		}
		if(s[i]=='U')
		{
			cnt[3]++;
			y = y + 1;
//			cout<<x<<" "<<y<<endl; 
			if(x==mx&&y==my)
			flag = 1 ;
			continue;
		}
		if(s[i]=='D')
		{
			cnt[4]++;
			y  = y - 1;
			if(x==mx&&y==my)
			flag = 1 ;
			continue;
		}
	}
		if(mx==0 && my == 0 )
		{
			cout<<"impossible"<<endl;
			return;
	}

		if(flag == 0 ) 
		{
			cout<<s<<endl;
			return ;
		}
		if(flag == 1 )
		{
			
			ll ansx = cnt[1] - cnt[2] ;
			ll ansy = cnt[3] - cnt[4] ; 
			if(ansx == mx && ansy == my )
			{	
				cout<<"Impossible"<<endl;
				return;
			}
			if( (mx == 0 &&ansx ==x && abs(my)<= abs(ansy)) || (my == 0 &&ansy == 0 && abs(mx)<= abs(ansx)))
			{
				cout<<"Impossible"<<endl;
					return;
			}
			while(cnt[1]--)
			{
				cout<<'R';
				if(cnt[2]!=0)
				{
					cout<<'L';
					cnt[2]--;
				}
			}
			while(cnt[2]--)
			{
				cout<<'L';
			}
			while(cnt[3]--)
			{
				cout<<'U';
				if(cnt[4]!=0)
				{
					cout<<'D';
					cnt[4]--;
				}
			}
			while(cnt[4]--)
			{
				cout<<'D';
			}
		}
		cout<<endl;
	} 

int main()
{
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	int tcase;
	cin>>tcase;
	while(tcase--)
	{
		slove();
	}
	return 0;
 }