instruction:
Given a category and a set of five words, find the word from the set that does not belong (i.e. is the least relevant) with the other words in the category. Words are separated by commas.
question:
Category: chocolate food 
Words: cake, fudge, rich, invent, cream
answer:
invent


question:
Category: personal characteristic 
Words: ethical, tropical, unflappalbe, cool, optimist
answer:
tropical


question:
Category: animals 
Words: hike, pig, horse, dog, duck
answer:

hike