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.

[EX Q]: Who has to push the rock up the hill?
[EX A]: Sisyphus

[EX Q]: Who wrote dont it make my brown eyes blue?
[EX A]: Richard Leigh

[EX Q]: Where are cannabinoid receptors located in the brain?
[EX A]:
Nerve Cells