Teacher: You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.
Teacher: Now, understand the problem? If you are still confused, see the following example:
Category: WHO'S BUYING? 
Clue: YouTube, in 2006
Solution: google
Reason: Google acquired, i.e. bought, YouTube in 2006 for $1.65 billion.

Now, solve this instance: Category: ABSOLUTELY NOTHING 
Clue: In math, a set containing no elements is called an empty set or this type
Student:
null set