A.Client issues an IGMP join after association with AP2, allowing AP2 to request a multicast stream from  Cisco WLC after AP1 issues an IGMP query.
B.Client issues an IGMP join after association with AP2, allowing AP2 to request a multicast stream from  Cisco WLC independent of AP1 multicast member status.
C.Client resumes multicast after association with AP2,  because multicast information is sent in mobility  exchanges and AP2 is already a member of the multicast group,  provided that another client has  already joined that multicast.
D.Client resumes multicast after association with AP2,  because multicast information is sent in mobility  exchanges and AP2 is already a member of the multicast group,  regardless if any other clients have  already joined that multicast.