You have an Exchange Server 2010 server named Server1. Server1 hosts a mailbox database named DB1 that contains 25 user mailboxes. You create a new public folder database named PUB2. You need to configure PUB2 as the default public folder database for each mailbox on DB1.  Which properties should you modify（）？ 

• A、Modify the properties of each mailbox.
• B、Modify the properties of DB1.
• C、Modify the properties of Server1.
• D、Modify the properties of PUB2.