Problems No 3. Studious Student

Studious Student You've been given a list of words to study and memorize. Being a diligent student of language and the arts, you've decided to not study them at all and instead make up pointless games based on them. One game you've come up with is to see how you can concatenate the words to generate the lexicographically lowest possible string.

InputAs input for playing this game you will receive a text file containing an integer N, the number of word sets you need to play your game against. This will be followed by N word sets, each starting with an integer M, the number of words in the set, followed by M words. All tokens in the input will be separated by some whitespace and, aside from N and M, will consist entirely of lowercase letters.

OutputYour submission should contain the lexicographically shortest strings for each corresponding word set, one per line and in order.

Constraints1 <= N <= 100
1 <= M <= 9
1 <= all word lengths <= 10


EXAMPLE … Shopee photos :

Facebook Hacker Cup 2011 Qualification Rounds Problems

Facebook Hacker Cup 2011 Qualification Rounds Problems

Competitors can log in to the competition website and attempt to solve the 3 problems anytime during the 72-hour period of the Qualification Round.

So, it will be a competition website is setup somewhere...
There will be 3 (three) question given.
Time available to solve those three question is just 72-hour. Shopee photos :