Which of the Following Definitions Represents Opt-In

Multiple Choice

Which of the following definitions represents opt-in?

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) Choosing to allow permission to incoming emails
D) Choosing to deny permission to incoming emails.