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.

[Q]: Category: SCIENCE 
Clue: What you're "stuck with" boiling down collagen, softening it with hot water & letting it swell
[A]: glue


[Q]: Category: EXPRESSIONS 
Clue: This positive expression used since the 1940s promotes a type of stove
[A]: "now you\'re cooking with gas"


[Q]: Category: BODY LANGUAGE 
Clue: Students know that this black opening in the center of the eye controls the amount of light that enters
[A]:
pupil