The managers of a certain office all have a Ph. D. , most of the Sichuan staff are not over 30 years old, and a small number of Sichuan staff have no PhD. Based on the above statement, which of the following can be derived? ['Some managers are over 30.', 'Some managers are under 30.', 'Some Sichuan staff are managers.', 'Some Sichuan staff are not managers.']