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

using namespace std;

const int N = 1e5 + 7;
int n,m,k;
int a[N],b[N];
char c[4] = {'U','L','R','D'};

void solve(){
	cin >> n >> m;
	string s; cin >> s;
	int len = s.size();
	map<char,int> mp;
	for(int i = 0;i < len;i ++){
		mp[s[i]] ++;
	} sort(c,c + 4);
	do{
		string cnt;
		for(int i = 0;i < 4;i ++){
			for(int j = 0;j < mp[c[i]];j ++){
				cnt += c[i];
			}
		} int flag = 0;
		int x = 0,y = 0;
		if(x == n && y == m) continue;
		for(int i = 0;i < len;i ++){
			if(cnt[i] == 'U') y ++;
			if(cnt[i] == 'D') y --;
			if(cnt[i] == 'L') x --;
			if(cnt[i] == 'R') x ++;
			if(x == n && y == m){
				flag = 1;
				break;
			}
		} if(flag) continue;
		else{
			cout << cnt << endl;
			return;
		}
	}while(next_permutation(c,c + 4));
	cout << "Impossible" << endl;
}

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