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-StartDate

B.
Get-MailboxActivityReport-Organization

C.
Get-MailboxActivityReport-Expression

D.
Get-MailboxActivityReport-EndDate

Explanation:
Use the Get-StaleMailboxDetailReport cmdlet to view mailboxes that haven’t been accessed for at
least 30 days.
The StartDate parameter specifies the start date of the date range.

Get-StaleMailboxDetailReport
https://technet.microsoft.com/en-us/library/jj200715(v=exchg.150).aspx