Which product and license type would meet all of these requirements?

Universal Containers, a new Salesforce customer, needs its millions of consumers to have public access to Knowledge on its corporate website. The consumers also need the ability to login to create, update, and read historical cases.

Which product and license type would meet all of these requirements?
A . Force.com Sites with Knowledge and Email-to-Case
B . Visualforce and Self-Service Portal
C . Force.com Sites with Knowledge and Web-to-Case
D . Force.com Sites and High-Volume Customer Portal

Answer: D