Phone A is able to dial the directory number of Phone B and complete a call. However, when Phone B dials the directory number of Phone A, Phone B receives a fast-busy tone. What is causing this issue?

A.	Phone A and Phone B are in different partitions.
B.	Phone B does not have Phone A in its partition.
C.	Phone B is not in the CSS of Phone A.
D.	Phone B does not have the CSS of Phone A in its partition.
E.	Phone B is not registered.
F.	Phone B has the incorrect CSS to dial Phone A.