D

#include <bits/stdc++.h>
typedef long long ll;
#define pb push_back
#define ff first
#define ss second
const int N=2e3+7;
const int mod=1e9+7;

int32_t main()
{
   ios_base::sync_with_stdio(false);
   cin.tie(0);

   int t;
   cin >> t;
   while(t--)
   {
        int n;
        cin >> n;

        char trump;
        cin >> trump;

        vector<string> cards,trumpCards;
        for(int i=0;i<2*n;i++)
        {
            string card;
            cin >> card;

            if(card[1]==trump)
                trumpCards.pb(card);
            else
                cards.pb(card);
        }

        vector< pair<string,string> > moves;
        for(int i=0;i<cards.size();i++)
        {
            for(int j=0;j<cards.size();j++)
            {
                if(i==j)
                    continue;
                if(cards[i]=="")
                    continue;
                if(cards[j]=="")
                    continue;

                if(cards[i][1]==cards[j][1])
                {
                    moves.pb({min(cards[i],cards[j]),max(cards[i],cards[j])});
                    cards[i]="";
                    cards[j]="";
                }
            }
        }

        bool ok=true;
        for(int i=0;i<cards.size();i++)
        {
            if(cards[i]!="")
            {
                if(trumpCards.empty())
                    ok=false;
                else
                {
                    moves.pb({cards[i],trumpCards.back()});
                    trumpCards.pop_back();
                }
            }
        }

        if(trumpCards.size()%2==1)
            ok=false;

        if(!ok)
        {
            cout << "IMPOSSIBLE\n\n";
            continue;
        }

        sort(trumpCards.begin(),trumpCards.end());
        for(int i=0;i<trumpCards.size();i++)
        {
            moves.pb({trumpCards[i],trumpCards.back()});
            trumpCards.pop_back();
        }

        for(auto ele : moves)
            cout << ele.first << " " << ele.second << "\n";
        cout << "\n";

   }
}