#include<stdio.h>
#include<string.h>
#include<string>
#include<list>

using namespace std;

int start[30];
int fin[30];
char firstword,finishword;
int size;

list<string> str[30];

void cal(int status){
    string now;
    int index;
    if(status == 1){
        for(int i=0;i<26;i++){
            if(start[i] > 0){
                now = "";
                now += str[i].front();
                str[i].pop_front();
                break;
            }
        }
    }
    else{
        now = str[firstword-'a'].front();
        str[firstword-'a'].pop_front();
    }
    size --;
    printf("%s ",now.c_str());

    while(size--){
        index = now[now.length()-1] - 'a';

        now = str[index].front();
        str[index].pop_front();
        printf("%s ",now.c_str());
    }
    printf("\n");

}

int possible(){
    int onfirst = 0, onfinish=0;
    for(int i=0;i<26;i++){
        if(start[i] != fin[i]){
            if(start[i] - fin[i] == 1){
                if(onfirst == 1)
                    return -1;
                onfirst=1;
                firstword='a'+i;
            }
            else if(start[i] - fin[i] == -1){
                if(onfinish == 1)
                    return -1;
                onfinish=1;
                finishword='a'+i;
            }
            else
                return -1;


        }
    }

    if(onfirst == 1)
        return 0;

    return 1;

}

int main(){
    int TC,num,posi;
    string tmpstr;
    char tmp[130];

    scanf("%d",&TC);


    while(TC--){
        for(int i=0;i<30;i++){
            start[i]=0;
            fin[i]=0;
            str[i].clear();
        }

        scanf("%d",&num);
        size = num;
        while(num--){
            scanf("%s",tmp);
            str[tmp[0]-'a'].push_back(tmp);
            start[tmp[0]-'a']++;
            fin[tmp[strlen(tmp)-1]-'a']++;
        }

        posi = possible();

        if(posi == -1)
            printf("IMPOSSIBLE\n");
        else
            cal(posi);
            //printf("possible\n");

    }

}