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

Category: WORLD HISTORY 
Clue: He completed vols. 2 & 3 of Karl Marx's "Das Kapital"
friedrich engels

Category: THE OLYMPICS OF 1980 
Clue: This man was elected president of the IOC just before the summer games; he's still there

juan antonio samaranch