#include<bits/stdc++.h>
using namespace std;
#define int long long

void solve(){
    int mx,my;cin>>mx>>my;
    string s;cin>>s;
    if(mx==0&&my==0){
        cout<<"Impossible\n";
        return;
    }
    map<char,int>mp;
    int y=0,x=0;
    for(auto i:s){
        mp[i]++;
        if(i=='U') y++;
        if(i=='D') y--;
        if(i=='L') x--;
        if(i=='R') x++;
    }
    if(x==mx&&y==my){
        cout<<"Impossible\n";
        return;
    }
    auto ch=[&](int nx,int ny){
        if(nx==mx&&ny==my) return true;
        else return false;
    };
    string ans="ULDR";
    string end;
    sort(ans.begin(),ans.end());
    do{
        int nx=0,ny=0,ok=1;
        //cout<<ans<<endl;
        for(int i=0;i<4;i++) {
            if (ch(nx, ny)) ok = 0;
            if (ans[i] == 'U') {
                int tem = mp['U'];
                while (tem--) {
                    ny++;
                    if (ch(nx, ny)) ok = 0;
                }
            } else if (ans[i] == 'R') {
                int tem = mp['R'];
                while (tem--) {
                    nx++;
                    if (ch(nx, ny)) ok = 0;
                }
            } else if (ans[i] == 'L') {
                int tem = mp['L'];
                while (tem--) {
                    nx--;
                    if (ch(nx, ny)) ok = 0;
                }
            } else if (ans[i] == 'D') {
                int tem = mp['D'];
                while (tem--) {
                    ny--;
                    if (ch(nx, ny)) ok = 0;
                }
            }
        }
        if(ok){
            end+=string(mp[ans[0]],ans[0]);
            end+=string(mp[ans[1]],ans[1]);
            end+=string(mp[ans[2]],ans[2]);
            end+=string(mp[ans[3]],ans[3]);
            break;
        }
    }while(next_permutation(ans.begin(),ans.end()));
    if(end.empty()){
        cout<<"Impossible\n";
    }else{
        cout<<end<<"\n";
    }
}

signed main(){
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int T=1;
    cin>>T;
    while(T--){
        solve();
    }
    return 0;
}