A. To set the primary contact on an account record when it is saved
Explanation:
After updating a Contact and then you set the Primary checkbox, the contact becomes the primary contact and this then updates the reference in the Parent Account. Triggers are used for this purpose and not workflow rule. In this case there is only one contact at a time that is set as Primary Contacts, and in the case where an Account does not have any Contacts, the first contact that is created is made the primary and the trigger sets that value in reference.
He could either use the tab key to indent, if you want to make the ruler visible, you can go to the view tab and click the check mark next to show ruler.
