Your network contains an Active Directory domain. The domain contains three domain  controllers. One of the domain controllers fails.  Seven days later， the help desk reports that it can no longer create user accounts. You need to  ensure that the help desk can create new user accounts.     Which operations master role should you seize（）

• A、domain naming master
• B、infrastructure master
• C、primary domain controller （PDC） emulator
• D、RID master
• E、schema master