You have an Exchange Online tenant.
You must identify mailboxes that are no longer in use.
You need to locate the inactive mailboxes.
Which Windows PowerShell command should you run?

A.
Get-StaleMailboxReport -Expression

B.
Get-StaleMailboxReport -Organization

C.
Get-MailboxActivityReport-Organization

D.
Get-StaleMailboxReport -EndDate

Explanation:
https://technet.microsoft.com/en-us/library/jj200763(v=exchg.160).aspx