You have an Exchange Server 2010 organization that contains 1,500 mailboxes. The
Average size of each mailbox is a 750 MB.
All users run either Microsoft Office Outlook 2010 or Outlook Web App to access their email.
All users who run Outlook 2010 are configured to use Cached Exchange Mode.
You need to configure a mailbox solution for the organization to meet the following
requirements:
Ensure that administrators can search and find any message
Reduce the size of the offline store (OST) for each user
Provide access to all e-mail messages by using either Outlook 2010 or Outlook Web App
What should you do?

A.
Create a Personal Archive for each user and then create a retention policy. Instruct users
to compact the OST file.

B.
Create a personal folder (PST) file for each user. Store all PST files on a network share.
Instruct users to compact the OST file.

C.
Create a second disabled user account and a second mailbox for each user. Configure
Journal rules to journal all the messages for each user to the user’s second mailbox.

D.
Create a new disabled user account and a new mailbox named Journaling Mailbox.
Configure journal rules to journal all the messages for each user to Journaling Mailbox.

Explanation:
There is only one possible answer to this: it cannot be a PST or a disabled user because
access must be available from OWA.
http://technet.microsoft.com/en-us/library/dd979795.aspx