#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define ios ios_base::sync_with_stdio(false);cin.tie(NULL)
#define ld long double
#define li __int128

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>; ///find_by_order(),order_of_key()
template<int D, typename T>struct vec : public vector<vec<D - 1, T>> {template<typename... Args>vec(int n = 0, Args... args) : vector<vec<D - 1, T>>(n, vec<D - 1, T>(args...)) {}};
template<typename T>struct vec<1, T> : public vector<T> {vec(int n = 0, T val = T()) : vector<T>(n, val) {}};
template<class T1,class T2> ostream& operator<<(ostream& os, const pair<T1,T2>& a) { os << '{' << a.f << ", " << a.s << '}'; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const deque<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1,class T2> ostream& operator<<(ostream& os, const map<T1,T2>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
int ri(){int x;scanf("%i",&x);return x;}
void rd(int&x){scanf("%i",&x);}
void rd(long long&x){scanf("%lld",&x);}
void rd(double&x){scanf("%lf",&x);}
void rd(long double&x){scanf("%Lf",&x);}
void rd(string&x){cin>>x;}
void rd(char*x){scanf("%s",x);}
template<typename T1,typename T2>void rd(pair<T1,T2>&x){rd(x.first);rd(x.second);}
template<typename T>void rd(vector<T>&x){for(T&p:x)rd(p);}
template<typename C,typename...T>void rd(C&a,T&...args){rd(a);rd(args...);}
//istream& operator>>(istream& is,__int128& a){string s;is>>s;a=0;int i=0;bool neg=false;if(s[0]=='-')neg=true,i++;for(;i<s.size();i++)a=a*10+s[i]-'0';if(neg)a*=-1;return is;}
//ostream& operator<<(ostream& os,__int128 a){bool neg=false;if(a<0)neg=true,a*=-1;ll high=(a/(__int128)1e18);ll low=(a-(__int128)1e18*high);string res;if(neg)res+='-';if(high>0){res+=to_string(high);string temp=to_string(low);res+=string(18-temp.size(),'0');res+=temp;}else res+=to_string(low);os<<res;return os;}

int ch(char c){
	if(c>='a'&&c<='z') return c-'a';
	else return 26+c-'A';
}
char ch(int a){
	if(a<26)return a+'a';
	return a-26+'A';
}
int main()
{
	int t=ri();
	while(t--){
		int n=ri();
		vector<pair<pair<int,int>,int>> cnt(n);
		for(int i=0;i<n;i++){
			for(int j=0;j<n;j++){
				int x=i*j;
				int a=x%n;
				int b=x/n;
				cnt[a].f.f++;
				if(b)
					cnt[b].f.s++;
				if(b&&a==b){
					cnt[a].s++;
				}
			}
		}
		//cout << cnt << endl;
		vector<string> a(n*n);
		rd(a);
		vector<pair<pair<int,int>,int>> cntChars(n);
		for(auto p:a){
			int a=ch(p.back());
			int b=sz(p)==1?0:ch(p[0]);
			cntChars[a].f.f++;
			if(sz(p)!=1)
				cntChars[b].f.s++;
			if(sz(p)!=1&&a==b){
				cntChars[a].s++;
			}
		}
		//cout << cntChars << endl;
		map<pair<pair<int,int>,int>,vector<int>> c;
		for(int i=0;i<n;i++){
			c[cnt[i]].pb(i);
		}
		vector<int> sol(n,-1);
		vector<int> rsol(n,-1);
		for(auto p:c){
			if(sz(p.s)==1){
				int j=-1;
				for(int k=0;k<n;k++){
					if(cntChars[k]==p.f){
						assert(j==-1);
						j=k;
					}
				}
				assert(j!=-1);
				sol[p.s[0]]=j;
				rsol[j]=p.s[0];
			}
		}
		map<vector<pair<int,int>>,int> mapa;
		for(int i=0;i<n;i++){
			if(sol[i]!=-1)continue;
			vector<pair<int,int>> myc(n);
			for(int a=0;a<n;a++){
				for(int b=0;b<n;b++){
					int x=a*b;
					int aa=x%n;
					int bb=x/n;
					if(bb==0)continue;
					if(aa==bb)continue;
					if(aa==i){
						if(sol[bb]!=-1){
							myc[bb].f++;
						}
					}
					if(bb==i){
						if(sol[aa]!=-1){
							myc[aa].s++;
						}
					}
				}
			}
			assert(mapa.count(myc)==0);
			mapa[myc]=i;
		}
		vector<vector<pair<int,int>>> charc(n,vector<pair<int,int>>(n));
		for(auto p:a){
			int a=ch(p.back());
			int b=sz(p)==1?0:ch(p[0]);
			if(sz(p)==1||a==b)continue;
			if(rsol[a]==-1&&rsol[b]!=-1){
				charc[a][rsol[b]].f++;
			}
			if(rsol[a]!=-1&&rsol[b]==-1){
				charc[b][rsol[a]].s++;
			}
		}
		for(int i=0;i<n;i++){
			if(rsol[i]==-1){
				int a=mapa[charc[i]];
				rsol[i]=a;
				sol[a]=i;
			}
		}
		for(int i=0;i<n;i++){
			printf("%c",ch(sol[i]));
		}
		printf("\n");
	}
	return 0;
}