You work as an Exchange Administrator for Xxx .The company has a Windows 2008 Active Directory-based network.The network contains an Exchange Server 2010 organization.An employee named John has recently left the company.You need to delete the mailbox and the user account for John.You also need to remove the mailbox from the Exchange database.Which of the following commands will you enter in the Exchange Management Shell to accomplish the task？（）

A、Delete-Mailbox -Identity john@TK.com

B、Remove-Mailbox -Identity john@TK.com -Permanent $true

C、Remove-Mailbox -Identity john@TK.com

D、Disable-Mailbox john@TK.com