#include<bits/stdc++.h>
using namespace std;
#define IOS std::ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
#define int long long
#define ull unsigned long long
#define fi first
#define se second
#define pi pair<int,int>

const int N=1e6+10;
const int INF=1e18;

int a[N];
int b[N];

map<char,int> mp;

void solve(){
    int x,y;
    cin>>x>>y;
    string s;
    cin>>s;
    if(x==0&&y==0){
        cout<<"Impossible\n";
        return;
    }
    mp.clear();
    for(int i=0;i<s.size();i++){
        mp[s[i]]++;
    }
    bool flag=0;
    string dir="DLRU";
    do{
        int xx=0,yy=0;
        for(int i=0;i<=3;i++){
            int t=mp[dir[i]];
            while(t--){
                if(dir[i]=='U') yy++;
                if(dir[i]=='D') yy--;
                if(dir[i]=='L') xx--;
                if(dir[i]=='R') xx++;
                if(xx==x&&yy==y){
                    flag=1;
                    break;
                }
            }
        }
        if(flag==0){
            string ss;
            for(int i=0;i<=3;i++){
                int t=mp[dir[i]];
                while(t--){
                    ss+=dir[i];
                }
            }
            cout<<ss<<"\n";
            return;
        }
    }while(next_permutation(dir.begin(),dir.end()));
    cout<<"Impossible\n";
}

signed main(){
    IOS
    int _=1;
    cin>>_;
    while(_--){
        solve();
    }
}