Which organization has line authority to oversee the management of multiple incidents being handled by separate incident command organizations?
a. area command
b. united command
c. multiagency command
d. joint command

Generally speaking, it would be a "Joint Command" that has line authority to oversee the management of multiple incidents being handled by separate Incident Command organizations, since in this case different agencies are "joined" together. 

If your answers look like this a) expansion through conquestb) development of a calendar c) development of a written language d) creation of a large road workthen the answer is dhope it