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: I GOT 3 As, MOM! 
Clue: In legend, this pure knight found the Holy Grail
galahad

Category: ON THE ROCKS 
Clue: This rock formed from hardened lava formed the Hawaiian Islands
basalt

Category: DENTISTRY 
Clue: As explained in the book "Marathon Man", it's "The inner substance of your teeth...where the nerves are"

pulp