What Permissions Are Required for a Marketer to Send an Email

What permissions are required for a marketer to send an email marketing message to a consumer in the EU?

A) A prior opt-in consent for consumers unless they are already customers.
B) A pre-checked box stating that the consumer agrees to receive email marketing.
C) A notice that the consumer's email address will be used for marketing purposes.
D) No prior permission required, but an opt-out requirement on all emails sent to consumers.