What sharing mechanism should be used to allow customers to view their own cases even after those cases are assigned to a support agent?

Universal Containers is implementing a customer community.

What sharing mechanism should be used to allow customers to view their own cases even after those cases are assigned to a support agent?
A . OWD and Apex Sharing
B. Sharing Set
C. Case co-ownership using Super User access
D. Sharing Map and custom permission set

Answer: B