Which of the Following Definitions Represents Opt-Out

Which of the following definitions represents opt-out?

A) A problem that occurs when someone registers purposely misspelled variations of well-known domain names.
B) The theft of a website's name that occurs when someone,posing as a site's administrator,changes the ownership of the domain name assigned to the website to another website owner.
C) Government attempts to control Internet traffic,thus preventing some material from being viewed by a country's citizens
D) Choosing to deny permission to incoming emails.