Except for the Hagfish,lamprey,and Their Close Relatives,all Vertebrates Have Paired

Except for the hagfish,lamprey,and their close relatives,all vertebrates have paired jaws; how did jaws evolve within an evolutionary clade that already had a skeleton?

A) A mutation causing extraskeletal cell division allowed the extra cells to form the jaws.
B) A modification of an existing skeletal element occurred; in this case, the gill arch was modified.
C) Reproduction between a nonjawed chordate and a jawed arthropod produced jawed offspring.
D) To date, biologists have been unsuccessful in explaining the origin of jaws.