How does this domain structure deviate from best practices?

Refer to the exhibit.

Shown is a diagram of the domain structure of an EMC Avamar server.

How does this domain structure deviate from best practices?
A . Domain2 should not be nested in another domain
B . Domain3 should have at least one client
C . ClientA should not be registered in the root domain
D . ClientB should not be in a domain that also contains a domain

Answer: C