Which Windows PowerShell command should you run next?

You are the Office 365 administrator for your company. The company uses Microsoft Exchange Online and Microsoft Lync Online.
An employee named User1 has the user name, email address, and Lync address [email protected].
The employee requests that you change only his Lync address to [email protected].
You start a Windows PowerShell session and run the following commands, providing your admin account credentials when prompted:

You need to complete the process of updating the employee’s Lync address without affecting any other addresses.
Which Windows PowerShell command should you run next?

A.
Set-Mailbox -Identity $ID -PrimarySmtpAddress $NewAddress

B.
Set-MsolUser -UserPrincipalName $ID –ProxyAddresses @{add=”$NewAddress”; remove=”$OldAddress”}

C.
Set-CsUser -Identity $ID –ProxyAddresses @{add=”$NewAddress”; remove=”$OldAddress”}

D.
Set-CsUser –Identity $ID –SipAddress $NewAddress

Explanation:
You can easily change the SIP address by running the Set-CsUser cmdlet:
Set-CsUser –Identity “Ken Myer” –SipAddress sip:[email protected]
Incorrect:
Not A: Set-Mailbox is used for Exchange Online and On-premises Exhange, but not for Lync.
Not B: Set-MsolUser is used for Azure, Office 365, and Windows Intune but not for Lync.
Not D: We need to change the SIP address, not the ProxyAddresses.
Modify the SIP Address of an Enabled Lync Server User
http://blogs.technet.com/b/nexthop/archive/2011/03/21/usermodifysip.aspx