TASK DEFINITION: In this task, you're given an open-domain question. Your task is to provide an answer to the given question. There is only one unique answer for each question. Your answer should be short, and refer to an entity, date, number, etc. Do not put your answer in the context of a sentence.
PROBLEM: Where does the water come from for victoria falls?

SOLUTION: Zambezi River

PROBLEM: How many episodes are in season 4 of agents of shield?

SOLUTION: 22

PROBLEM: The ultimate source of new variation in nature is?

SOLUTION:
Random mutations