#include <fstream>

#define I_F "balls.in"
#define O_F "balls.out"

const short Maxn=7*2;
const short Maxstep=10;

std::ifstream fin(I_F);
std::ofstream fout(O_F);

struct lb
{
	short s[Maxn];
	short d, l, x;
	lb *prep, *succ;
};

short m,n;
short s[Maxn];
short ansn, ans[Maxstep][Maxn];
bool flag;

inline void Input();
inline bool Ok(const short*);
inline void Copy(const short*, short*);
inline short L(const short, const short);
void Delete(lb*);
bool Search();
inline void Output();

int main()
{
	fin>>m;
	for (short i=0; i<m; i++)
	{
		Input();
		flag=Search();
		Output();
	}
	fin.close();
	fout.close();
}

inline void Input()
{
	fin>>n;
	short fix=0;
	char t=fin.get();
	for (short i=0; i<n*2-1; i++)
	{
		t=fin.get();
		if (t=='a')
			s[i+fix]=1;
		else if (t=='b')
			s[i+fix]=2;
		else
			s[i]=s[i+1]=0,
			fix=1;
	}
	t=fin.get();
}

inline bool Ok(const short *s)
{
	short j=0;
	for (short i=0; j<n-1; i++)
		if (s[i]==1)
			j++;
		else if (s[i]==2)
			return false;
	return true;
}

inline void Copy(const short *a, short *b)
{
	for (short i=0; i<n*2; i++)
		b[i]=a[i];
}

inline short L(const short a, const short b)
{
	return (a!=b)?((a==1)?0:1):((a==1)?2:3);
}

void Delete(lb *x)
{
	if (x->succ!=NULL)
		Delete(x->succ);
	delete x;
}

bool Search()
{
	if (Ok(s))
	{
		Copy(s,ans[0]);
		ansn=0;
		return true;
	}
	lb *head, *tail;
	head=new lb;
	head->prep=head->succ=NULL;
	head->d=0;
	head->l=-1;
	Copy(s,head->s);
	for (head->x=0; head->s[head->x]>0; head->x++);
	tail=head;
	
	for (lb *temp=head; temp!=NULL; temp=temp->succ)
		for (short i=0; i<n*2-1; i++)
			if (temp->s[i]*temp->s[i+1]>0 && L(temp->s[i],temp->s[i+1])!=temp->l)
			{
				tail->succ=new lb;
				tail=tail->succ;
				tail->prep=temp;
				Copy(temp->s,tail->s);
				tail->s[temp->x]=tail->s[i];
				tail->s[temp->x+1]=tail->s[i+1];
				tail->s[i]=tail->s[i+1]=0;
				tail->d=temp->d+1;
				tail->l=L(temp->s[i],temp->s[i+1]);
				tail->x=i;
				
				if (Ok(tail->s))
				{
					ansn=tail->d;
					for (lb *j=tail; j!=NULL; j=j->prep)
						Copy(j->s,ans[j->d]);
					Delete(head);
					return true;
				}
				if (tail->d>Maxstep)
				{
					Delete(head);
					return false;
				}
			}
	Delete(head);
	return false;
}

void Output()
{
	if (flag)
		for (short i=0; i<=ansn; i++)
		{
			fout<<i<<' ';
			for (short j=0; j<n*2; j++)
				if (s[j]==1)
					fout<<'a';
				else if (s[j]==2)
					fout<<'b';
				else
					fout<<' ',
					j++;
			fout<<std::endl;
		}
	else
		fout<<"NO SOLUTION\n";
}