A computer virus infects a large number of computers at a sensitive government department. The department officials identify a single floppy disk as the source of the Intection. The floppy disk was circulated among all of the staff members, who each infected their own computer when they loaded the disk into their computer. To track the clrculation of the infecting disk, a graph is drawn where verfices represent staff members with infected computers and edges connect each person to the statff member from whom the person first received the disk. Must the graph necessarily be a tree? A) NO B) Yes