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.

Category: YOU GET AN "F" 
Clue: This type of cable contains threads of glass that transmit signals in the form of pulses of light
fiber optic

Category: LESSER-KNOWN PROVERBS 
Clue: It specifically "tries truth" as well as generally "tries all things"
time

Category: LITERARY PAIRS 
Clue: Absurdly enough, Tom Stoppard re-dramatized this Shakespearean duo, old school chums of Hamlet turned spies

rosencrantz & guildenstern