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: PARTICLE PHYSICS 
Clue: To get an element's mass number, add its protons & these
neutrons

Category: SINGERS 
Clue: "Life Is A Cabaret" for this star who was 19 when she won a Best Actress Tony for "Flora, The Red Menace"
liza minnelli

Category: DON'T LOSE YOUR TRAIN OF THOUGHT 
Clue: The Grand Traverse Dinner Train specializes in tours of this duration, so let's invite Gilligan

3 hours