What happens if no currency is set on an account?

1. A currency must be set on an account.

2. The account automatically defaults to the company’s currency if no currency is set.

3. If no currency is set, the account can be used with any currency. (correct answer as Odoo advised)

Dear Odoo Community,  

I don't agree with the answer on this question. If no currency is set on an account, it should get the defaults to the company's currency.