'are keys' or 'are a key'?

[Nataliia_Daisy]

Hello, dear coaches!!!
Could anyone tell me how is it right to say:
1) Persistence and determination are keys to success; or 2) persistence and determination are a key to success?
Thank you very much!

[Mister Micawber]

Try this (someone else already has, here: Questions! What's the difference between I have difficulty in finding the place ):

Persistence and determination are key to success.
_________________
Native English teacher at Mister Micawber's

[Nataliia_Daisy]

Thanks!!