You have an Exchange Server 2010 server.You need to prevent users from accessing public folders by using Outlook Web App （OWA）.Your solution must not prevent users from accessing public folders by using Office Outlook. Which two actions should you perform？（）

• A、Create a managed folder mailbox policy.
• B、Modify the properties of the OWA virtual directory.
• C、Modify the default Outlook Web App Mailbox policy.
• D、Modify the properties of the public folder database.