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: ISLAND NATIONS 
Clue: It's where the mambo originated
cuba

Category: O FOR A 
Clue: Completely humble yourself for small stones & pebbles
grovel for gravel

Category: SHIPS 
Clue: It has surpassed Liberia as the country with the most merchant ships under its flag

panama