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.

What's the zip code for o'fallon missouri?
63366, 63368

Which is the new member of nato in 2017?
Montenegro

Green house gases which is present in very high quantity is?

Water vapor