What is the difference between a literary ballad and a folk ballad?

What is the difference between a literary ballad and a folk ballad?

a. Folk ballads were written by monks and pages long ago who kept their names secret.
b. Folk ballads are always sung; literary ballads are never put to music.
c. A folk ballad has been passed down orally; a literary ballad has a known author.
d. Folk ballads use common people for their characters; literary ballads are about royalty.