DRAG DROP
You have an Exchange Server 2013 organization that contains five servers.
Several employees plan to use Microsoft Outlook to collaborate on some projects.
You need to configure access to Outlook to meet the following requirements:
Several employees must be able to send email messages as a user named User1.
Several employees must be able to send email messages on behalf of a user named User2.
Which cmdlets should you use?
To answer, drag the appropriate crndlet to the correct requirement in the answer are
a. Each crndlet may be used once, more than once, or not at all. Additionally, you may need to drag
the split bar between panes or scroll to view content.
Answer: 
This is right.
The way I remember how to set send as permissions is that if you do it manually you have to go into AD and add it into the security tab of a user, therefore adding AD permissions.
Then the send on behalf of option would make sense to be either add-mailboxpermission or set-mailbox (add-mailboxfolderpermission is just for folders).
However the correct answer is set-mailbox -grantsendonbehalfto (or something similar)