which one is the right:
"everyone/everybody says" or
"everyone/everybody say"?

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The first one is correct as a number of people are saying it. So the plural 's' gets put on the verb, however something needs to be added after the says. For example, 'Everybody says good morning to me' or 'Everybody says it's going to rain tomorrow'.
You would use this when you are talking about what other people have said.

However, you could use the second sentence as well, but something would have to come after say. For example, 'everybody say Hello' or 'everybody say thank you'
You would use this when you are asking or telling people to say something