Congratulations

As you know, the position for which you are applying requires superlative problem-solving skills in a variety of arenas, and the ability to think critically on the fly is essential. To evaluate your ability in this area, the practical portion of the interview process consists of a series of locked-room puzzles. You will need to use all of your ingenuity to find the key to unlocking each room. There are six rooms total; four of the rooms will have individual time limits, while the remaining two rooms will be untimed. You will be observed by the interview team from a remote location, and your progress through the rooms will be recorded. For which type of communication would this paragraph be used?

A)casual note
B)informal email
C)formal business