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.

Who is the best selling novelist of all time?
Dame Agatha Mary Clarissa Christie, Lady Mallowan, DBE

When does the rpdr season 9 finale air?
June 23, 2017

What's the name for earth's supply of water?

hydrosphere