What permission is granted to Customers when invited to Chatter Group?

Universal Containers would like to collaborate with its customers within Salesforce, and has decided to enable the "Allow Customer Invitations" Chatter setting.

What permission is granted to Customers when invited to Chatter Group?
A . The ability to invite members to groups of which they are a member
B . The ability to @mention accounts of which they are a contact.
C . The ability to request access to public groups
D . The ability to interact with members of their groups

Answer: D