instruction:
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.
question:
Category: PARTICLE PHYSICS 
Clue: To get an element's mass number, add its protons & these
answer:
neutrons


question:
Category: "R"ITERS 
Clue: This author of the hitchhiking novel "Even Cowgirls Get the Blues" once hitchhiked across the U.S.
answer:
tom robbins


question:
Category: BEGINS & ENDS IN "N" 
Clue: Last name of "Boy Genius" Jimmy who starred in his own animated feature film in 2001
answer:

neutron