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 consistency, answers should be in all lower cased letters.

Q: Category: LETHAL WEAPONS 
Clue: In the largest man-made explosion in history, the USSR detonated a 50-megaton one of these in 1961

A: a hydrogen bomb
****
Q: Category: LARGE EQUIPMENT 
Clue: For smooth travel, ballast tampers & ballast regulators keep the gravel at the right level among these

A: railroad tracks
****
Q: Category: KINGS & QUEENS 
Clue: Ancient Macedonia had 5 kings with this name; one came immediately before Alexander the Great & one immediately after

A:
philip
****